Prep the oven and pan: Heat oven to 400°F (200°C). Lightly oil a 9x13-inch baking dish or similar casserole.

Slice the veg: Cut zucchini into thin rounds (about 1/8–1/4 inch). Slice the onion thinly. Mince the garlic.

Season the chicken: Pat dry and slice breasts horizontally into cutlets for even cooking. Season both sides with salt, pepper, and half the Italian seasoning.

Sear the chicken: Heat 1 tablespoon olive oil in a large skillet over medium-high. Sear chicken 2–3 minutes per side until lightly golden but not fully cooked. Transfer to a plate.

Soften the zucchini: Add another tablespoon of oil. Sauté zucchini in batches with a pinch of salt, 2–3 minutes per side, just to drive off moisture and get a little color. Remove to a tray.

Cook the onions and garlic: Add the remaining oil if needed. Sauté onion over medium heat for 3–4 minutes until translucent. Stir in garlic for 30 seconds.

Make a quick sauce: Add crushed tomatoes (if using), cream, remaining Italian seasoning, crushed red pepper, lemon zest, and a pinch of salt and pepper. Simmer 2–3 minutes until slightly thickened. Taste and adjust seasoning.

Layer the casserole: Spoon a thin layer of sauce into the baking dish. Add a layer of zucchini, a scatter of onions, and a sprinkle of Parmesan. Place chicken cutlets on top, then spoon more sauce over them. Finish with remaining zucchini, sauce, mozzarella, and the rest of the Parmesan.

Bake: Cover loosely with foil and bake 15 minutes. Remove foil and bake another 10–15 minutes until the top is golden and the chicken reaches 165°F (74°C).

Rest and garnish: Let it sit 10 minutes so it sets. Finish with lemon juice and chopped basil or parsley.

Serve: Slice into squares. Pair with a simple green salad or steamed green beans.