Preheat your oven. Set it to 375°F (190°C). Lightly grease a 9×13-inch baking dish with olive oil.
Cook the aromatics. In a large skillet over medium heat, add olive oil. Sauté the onion for about 3–4 minutes until softened, then add garlic and cook for another minute (careful not to burn it — burnt garlic ruins everything).
Brown the turkey. Add ground turkey and cook until no longer pink, breaking it apart with a spoon. This should take 5–6 minutes.
Add flavor. Stir in the diced tomatoes, Italian seasoning, salt, and pepper. Let the mixture simmer for about 5 minutes to let the flavors come together.
Layer it up. Spread half the zucchini slices on the bottom of your casserole dish. Top with half of the turkey mixture, then half the cheese. Repeat with the remaining zucchini, turkey, and cheese. Sprinkle breadcrumbs over the top if you like a crispy finish.
Bake to perfection. Place uncovered in the oven and bake for 30–35 minutes, until the top is bubbly and golden brown.
Rest before serving. Let it sit for 10 minutes before cutting — this helps everything firm up (and saves you from burning your tongue).
