Preheat the oven to 400°F (200°C). Lightly coat a 9x13-inch baking dish with nonstick spray.
Sauté the veggies. In a large skillet, warm olive oil over medium heat.
Add onion, bell pepper, and mushrooms. Cook 5–7 minutes until softened and any mushroom moisture cooks off. Stir in garlic for 30 seconds.
Brown the turkey. Push veggies to the side of the pan and add ground turkey.
Season with salt, pepper, Italian seasoning, and red pepper flakes. Cook, breaking it up, until no longer pink and lightly browned, about 6–8 minutes.
Wilt the greens. Stir in spinach and cook just until wilted, 1–2 minutes. Taste and adjust salt and pepper.
Add the sauce. Pour in the pizza sauce and simmer 2–3 minutes to meld flavors.
You want a thick, scoopable mixture—not soupy.
Assemble the bake. Spread the turkey mixture in the prepared baking dish. Top with mozzarella and Parmesan. Add pepperoni slices and olives if using.
Bake. Place on the center rack and bake 12–15 minutes, until the cheese is melted and bubbling.
Broil for color. If you like golden, spotty cheese, switch to broil for 1–2 minutes.
Watch closely.
Rest and garnish. Let it sit 5 minutes so it sets up. Sprinkle with fresh basil or parsley.
Serve. Spoon into bowls. Add a side salad or garlic toast if you want something extra.