In a large skillet, heat the olive oil over medium heat. Add the chopped onion and garlic, sautéing for about 2-3 minutes until they become fragrant and translucent.
Add the ground turkey to the skillet, breaking it apart with a spatula. Cook until browned and cooked through, about 5-7 minutes. Drain excess grease if necessary.
Stir in the diced zucchini and halved cherry tomatoes into the turkey mixture. Cook for another 3-4 minutes until the zucchini is slightly tender.
Add the marinara sauce, Italian seasoning, salt, and black pepper. Mix everything together well and let it simmer for a couple of minutes to allow the flavors to meld.
Transfer the turkey and vegetable mixture into a greased 9x13 inch baking dish, spreading it out evenly.
Sprinkle the shredded mozzarella cheese evenly over the top, followed by the grated Parmesan cheese.
Place the baking dish in the preheated oven and bake for about 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes before garnishing with fresh basil leaves. Serve warm.