Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the cooked chicken, sliced zucchinis, cherry tomatoes, minced garlic, oregano, basil, salt, pepper, and red pepper flakes if using. Drizzle with olive oil and toss until everything is well coated.
Spread the chicken and vegetable mixture evenly in a greased 9x13-inch baking dish.
Sprinkle the mozzarella and Parmesan cheese evenly over the top of the mixture.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes. Garnish with fresh basil if desired before serving.