1. Preheat oven to 375°F (190°C). Grease a 9×13-inch casserole dish with olive oil.
2. Heat olive oil in a large skillet over medium heat. Add cubed chicken and minced garlic. Cook until chicken is no longer pink, about 5 to 6 minutes.
3. Add sliced zucchini. Cook 5 minutes until slightly tender but still holding shape. Season with salt, pepper, and thyme.
4. Whisk together chicken broth and heavy cream. Pour into skillet and simmer 5 minutes.
5. Stir in half the mozzarella and half the Parmesan until melted and smooth.
6. Transfer to the prepared casserole dish. Top with remaining mozzarella and Parmesan.
7. Bake 20 to 25 minutes until cheese is bubbly and golden.
8. Rest 5 minutes, garnish with parsley, and serve.

Nutrition Information (Per Serving)

• Calories: 310
• Carbohydrates: 6g
• Protein: 28g
• Fat: 19g
• Fiber: 1g
• Sodium: 420mg
• Calcium: 220mg (17% DV)
• Vitamin C: 14mg (16% DV)

Note: Nutrition estimates are based on 6 servings. Values will vary based on the chicken size and cheese brands used.

Notes

• Cook zucchini only 5 minutes in the skillet — overcooking makes it turn to mush in the oven.
• Don’t overcook the chicken in the skillet — it finishes cooking in the oven.
• Use heavy cream, not milk — milk is too thin for the proper creamy sauce.
• Rest 5 minutes after baking so the sauce settles and the casserole scoops cleanly.

Storage Tips

• Refrigerator: Store in an airtight container for up to 3 days.
• Reheating: Cover with foil and warm at 325°F for 15 minutes, or microwave individual servings covered.
• Make-ahead: Assemble without top cheese, refrigerate up to 24 hours, add cheese just before baking.
• Freezer: Freeze unbaked without top cheese for up to 2 months; thaw overnight and add fresh cheese before baking.

Serving Suggestions

• As a complete one-dish dinner with a side salad
• With garlic bread or crusty Italian bread alongside
• Over rice or pasta for a heartier presentation
• With roasted potatoes for a full plate

Mix It Up (Recipe Variations)

Italian: Add Italian seasoning and replace half the mozzarella with provolone.

Bacon: Cook chopped bacon first; cook chicken in bacon fat and add bacon back with zucchini.

Lemon Herb: Add lemon zest to the cream; stir in fresh basil or dill at the end.

Tomato: Add halved cherry tomatoes with the zucchini for bursts of sweet acidity.

What Makes This Recipe Special

The brief sauté of zucchini before baking is what prevents this chicken and zucchini casserole from becoming watery — a common problem with summer squash casseroles. When zucchini is cut and exposed to heat, its cell walls begin to break down and release water. The 5-minute skillet step allows much of this moisture to evaporate before the zucchini goes into the casserole dish, concentrating its flavor and ensuring the final dish has a creamy sauce rather than a watery one. This pre-cooking technique is why the casserole maintains its creamy consistency even after baking, while casseroles made with raw zucchini often end up swimming in liquid.