This chicken and zucchini gratin is a baked family-style casserole made with diced chicken, sautéed zucchini, sweet potatoes, a creamy chicken sauce, fresh basil, and melted mozzarella. It is different from a classic potato gratin because it is more complete: protein, vegetables, sauce, and cheese all in one dish. I make it when I want something comforting without making a separate meat, side, and sauce.

This recipe is based on my YouTube video, with a few adjustments since publication. The main change is precision. In the video, everything is cooked by eye, but for the website version I prefer to give clearer quantities so the gratin does not turn watery or too heavy. The mistake to avoid is adding zucchini that has not released enough moisture. If the zucchini goes into the dish too raw, the bottom of the gratin can become liquid instead of creamy.

What I look for here is a sauce that coats the chicken, not a thin soup. When the chicken and sauce go into the bowl with the sweet potatoes and zucchini, the mixture should look creamy and generous, but not swimming. The cheese on top should melt into a golden layer, and when you serve a portion, it should hold together enough to scoop cleanly.

Easy Creamy Chicken and Zucchini Gratin with Sweet Potatoes

Why I Make It This Way

I make it this way because sweet potatoes bring a softer, slightly sweet base that works well with chicken and zucchini. Regular potatoes are great, but sweet potatoes give the gratin a different texture and color. They also help make the dish feel hearty without needing pasta or rice.

I prefer to cook the main components separately before assembling. The sweet potatoes are boiled until just tender, the zucchini is sautéed over high heat, and the chicken simmers in its sauce. It is one extra step compared with dumping everything into a dish, but it gives a better result. The zucchini gets a little color, the chicken stays moist, and the sauce has time to thicken before going into the oven.

This is also what separates this recipe from a classic vegetable-only gratin like my creamy zucchini gratin. That one is more of a side dish. This version is a full dinner. It is also less pasta-heavy than a creamy baked chicken pasta and less traditional than a classic potato gratin. Same comfort food family, different purpose.

Ingredients That Matter

The chicken can be breast or boneless skinless thighs. Breast gives a cleaner, lighter texture, while thighs stay a little juicier. If you are not sure which cut to use, my guide to chicken cuts explains the difference between breast, thighs, and drumsticks.

The sweet potatoes should be cut into medium chunks. Not too small. If the pieces are tiny, they break apart when mixed with the sauce. You want them tender, but still recognizable in the finished gratin.

The zucchini needs special attention. Cook it in a hot pan with a little oil, salt, and pepper until you see light browning on the edges. If the pan is crowded and the zucchini steams, it will release water later in the baking dish. The sound in the pan should be a gentle sizzle, not a wet simmer.

For the sauce, I use chicken broth, cream, and a flour-based thickener. Homemade broth gives the best flavor, and if you keep some in the freezer, this is a good place to use it. You can also use homemade chicken bouillon cubes for a quick base.

The sauce is not exactly a béchamel, but it behaves a little like one. If you want more detail on that style of cooking, my guide on how to make a creamy sauce is useful. If your sauce looks too loose, check my tips on how to thicken a sauce before assembling the gratin.

Step-by-Step Instructions

Start with the cheese. Grate the mozzarella and keep it cold while the rest of the recipe is prepared. Freshly grated cheese melts better than pre-shredded cheese, but either works if that is what you have.

Peel the sweet potatoes and cut them into medium chunks. Place them in a large pot, cover with cold salted water, and bring to a boil. Once the water boils, cook until the pieces are just tender when pierced with a knife. This usually takes 12 to 18 minutes depending on the size. Do not cook them until they collapse. Drain and keep them warm.

While the sweet potatoes cook, prepare the vegetables. Slice or dice the onions. Mince the garlic. If garlic tends to burn on you, it helps to read through my method for mincing garlic without burning it. For the onions, even cuts help them soften evenly, just like in my guide on how to cut an onion.

Cut the zucchini into chunks. Heat a large skillet with oil over medium-high heat. Add the zucchini, season with salt and pepper, and cook until lightly browned. If liquid gathers in the skillet, let it evaporate or drain it off. The zucchini should look glossy, lightly colored, and not mushy. Transfer it to a large mixing bowl with the sweet potatoes.

In the same or another large skillet, cook the diced chicken in a little oil. Let it take some color before stirring too much. Add the onions and cook until they soften. Add the garlic near the end so it does not burn. Season with salt and pepper.

Sprinkle in the flour with a little fat and stir so it coats the chicken and onions. Pour in the chicken broth gradually, stirring as you go. The sauce will look thin at first, then it will start to thicken as it simmers. Add the cream and cook until the sauce coats a spoon. At this point, it should look creamy and smooth, not watery.

The chicken should be fully cooked before the gratin goes into the oven. For safety, chicken should reach the proper internal temperature. I keep a thermometer close by, and my chicken internal temperature guide is the reference I use when timing feels uncertain.

Add fresh basil to the sauce at the end, then pour the chicken and sauce into the bowl with the sweet potatoes and zucchini. Mix gently. The sweet potatoes are tender, so do not crush everything. Transfer to a baking dish and spread it evenly.

Cover with mozzarella, making sure to get cheese into the corners. Bake until the center is hot and the edges bubble. Then broil briefly to brown the top. Stay close at the end. Cheese can go from golden to too dark very quickly.

How This Recipe Fits the Site

This recipe belongs in the creamy chicken dinner family, but it has its own place. It is not a skillet dinner like many quick chicken recipes. It is not a pasta bake. It is not just a vegetable gratin. It is a full oven-baked meal with chicken, zucchini, sweet potatoes, sauce, and cheese.

For faster chicken ideas, the easy chicken dinner collection makes more sense. For oven-style meals, the baked chicken recipe collection is closer. For rich, saucy comfort food, this gratin sits naturally beside the creamy chicken recipe collection.

It is hearty enough for cold weather, but it still works in summer when zucchini is everywhere. That is what I like about it. It does not feel locked to one season.

Substitutions

Use chicken thighs instead of chicken breast if you want a juicier result. They are more forgiving and stay tender even if the gratin spends a few extra minutes in the oven.

Use regular potatoes instead of sweet potatoes if you want a more traditional flavor. In that case, boil them until just tender and season a little more because regular potatoes are less sweet.

Use cheddar, Monterey Jack, provolone, or a mix of mozzarella and Parmesan instead of mozzarella alone. Mozzarella gives stretch and softness. Parmesan gives salt and sharper flavor.

Use half-and-half instead of cream if needed. The sauce may be slightly lighter, so simmer it until it coats the spoon before assembling.

Use cornstarch instead of flour if you need a gluten-free thickener. Mix it with a little cold broth first, then add it to the simmering sauce. Do not add dry cornstarch directly to the pan.

Use parsley instead of basil if basil is not available. The taste will be less summery, but it still works.

What to Serve With It

This gratin is already a full meal, so I keep sides simple. A crisp salad is enough. A classic Greek salad gives freshness beside the creamy sauce, and a simple lemon vinaigrette cuts through the cheese nicely.

For a bigger table, roasted vegetables work well because they keep the same oven-dinner feeling. I would serve it with oven-roasted mixed vegetables or, if you want more sweet potato on the side for a crowd, air fryer sweet potatoes are easy to make separately.

If you want another comforting chicken dish for the same kind of family meal, try a classic chicken pot pie another night. It has the same cozy spirit, but with pastry instead of a cheese topping.

FAQ

Can I make this gratin ahead of time?

Yes. Assemble it, cover it, and refrigerate it for up to 24 hours. Add extra baking time if it goes into the oven cold. I prefer to bake it covered first, then uncover and broil the cheese at the end.

Why is my gratin watery?

The zucchini probably released too much moisture, or the sauce was too thin before baking. Cook the zucchini over high heat and thicken the sauce until it coats the spoon before mixing everything together.

Can I use rotisserie chicken?

Yes, but add it after the onions and sauce are made. Since it is already cooked, you only need to warm it through. This is a good shortcut for a weeknight casserole.

Can I freeze it?

You can, but zucchini changes texture after freezing. The flavor will still be good, but the sauce may loosen slightly when reheated. Reheat it uncovered in the oven so extra moisture can evaporate.

How do I know when it is ready?

The edges should be bubbling, the center should be hot, and the cheese should be melted and golden. If the top browns before the center is hot, cover it loosely with foil and keep baking.