In a large skillet over medium heat, add the ground turkey or chicken. Cook until browned, breaking it apart with a spoon, about 5-7 minutes.
Once the meat is cooked, add the diced onion and minced garlic to the skillet. Sauté until the onion becomes translucent, about 3-4 minutes.
Stir in the diced bell pepper, crushed tomatoes, tomato paste, Italian seasoning, and oregano. Season with salt and pepper to taste. Simmer for about 10 minutes until slightly thickened.
While the sauce is simmering, take the sliced zucchini and lay it out on a clean kitchen towel. Sprinkle with a little salt and let it sit for 10 minutes to draw out excess moisture. After 10 minutes, pat the zucchini slices dry.
In a greased 9x13 inch casserole dish, layer half of the zucchini slices on the bottom. Pour half of the meat sauce over the zucchini, followed by half of the mozzarella and Parmesan cheese.
Repeat the layers with the remaining zucchini, meat sauce, and cheeses.
Cover the casserole dish with aluminum foil (to prevent the cheese from burning) and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown.
Remove from oven and let it rest for about 5-10 minutes. Garnish with fresh basil leaves if desired before serving.
Notes
Let the casserole rest before serving for better slicing.