Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with olive oil to prevent sticking and promote even browning.
Sauté chopped onion and minced garlic in olive oil over medium heat until fragrant, about 2 minutes.
Brown the ground turkey in the skillet, breaking it apart with a spoon until fully cooked and no longer pink, about 5-6 minutes.
Combine diced tomatoes, dried Italian herbs, salt, and black pepper into the turkey mixture; let it simmer for about 3-4 minutes.
Layer half of the zucchini slices in the greased baking dish, followed by half of the turkey mixture, and then half of the mozzarella cheese; repeat these layers.
Bake uncovered for 30-35 minutes until cheese is bubbly and golden brown. Let it cool for 5 minutes before serving.