Preheat your oven to 375°F (190°C).

Grease a 9×13-inch baking dish with olive oil.

In a large skillet over medium heat, add olive oil and sauté the chopped onion and minced garlic for about 2 minutes until fragrant and the onion is translucent.

Add the ground turkey to the skillet and cook for about 5-6 minutes, breaking it up with a spoon until browned.

Stir in the drained diced tomatoes, Italian herbs, salt, and black pepper. Let it simmer for about 3-4 minutes.

In the prepared baking dish, layer half of the sliced zucchini, top with half of the turkey mixture, and sprinkle with half of the mozzarella cheese. Repeat the layers.

Bake uncovered for 30-35 minutes, or until the casserole is bubbly and the cheese is golden.

Allow the casserole to cool for about 5 minutes before serving.