Preheat your oven to 375°F (190°C) and generously grease a 9×13-inch baking dish with olive oil.
In a large mixing bowl, combine the chicken breasts, sliced zucchini, halved cherry tomatoes, sliced red onion, and minced garlic. Drizzle with olive oil and add all seasonings (oregano, basil, smoked paprika, salt, black pepper, and optional red pepper flakes). Toss everything together until evenly coated.
Spread the mixture evenly in the prepared baking dish, arranging chicken breasts so they don't overlap. Nestle vegetables around and on top of chicken. Sprinkle mozzarella and Parmesan evenly over everything.
Cover tightly with aluminum foil and bake for 20 minutes. Remove foil and continue baking for 10-15 minutes until cheese is golden brown and bubbly and chicken reaches an internal temperature of 165°F (75°C).
Let the dish rest for about 5 minutes before serving. Garnish with fresh chopped parsley.
