Preheat your oven to 375°F (190°C) and prepare a baking dish.

In a skillet, sauté finely chopped onion and minced garlic in olive oil for 3-4 minutes until soft.

In a mixing bowl, combine shredded cooked chicken, sautéed onion and garlic, sour cream, mayonnaise, Italian seasoning, salt, and pepper.

Gently fold in thinly sliced zucchini along with half of the cheddar and Parmesan cheeses.

Transfer the mixture into the greased baking dish and top with remaining cheese.

Bake uncovered for 25-30 minutes until the top is golden brown and bubbling.

Let the casserole rest for about 5 minutes before serving.

Garnish with freshly chopped parsley or basil before serving.