Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish with olive oil or non-stick spray.

Heat one tablespoon of olive oil in a large skillet over medium-high heat. Add the diced onion and cook for 3 to 4 minutes until translucent.

Add the minced garlic to the skillet and cook for another minute until fragrant.

Add the ground turkey to the skillet. Break it apart with a wooden spoon and cook until it is no longer pink. Drain any excess liquid from the pan.

Stir in the marinara sauce, dried oregano, dried basil, and red pepper flakes. Season with salt and pepper. Let the sauce simmer on low heat for about 5 to 7 minutes to blend the flavors.

Place a single layer of zucchini slices at the bottom of the prepared baking dish.

Spread half of the meat sauce over the zucchini layer. Sprinkle with half of the mozzarella cheese.

Add another layer of zucchini slices on top, followed by the remaining meat sauce.

Top the casserole with the remaining mozzarella and the grated Parmesan cheese.

Bake in the preheated oven for 25 to 30 minutes. The cheese should be melted and bubbly, and the zucchini should be tender when pierced with a fork.

Remove from the oven and let it rest for 5 to 10 minutes before serving. Garnish with fresh parsley.