Heat oven to 375°F. Bring a large pot of salted water to a boil.
Boil the pasta until very al dente, about 2 minutes shy of package directions. Drain and set aside.
Warm 1 tbsp olive oil in a large skillet over medium heat. Soften the onion for 4–5 minutes.
Stir in the garlic and cook 30 seconds until fragrant.
Add the turkey and cook, breaking it up, until browned. Season with salt, black pepper, Italian seasoning, and red pepper flakes.
Pour in the marinara and simmer 3–4 minutes to meld flavors.
Combine pasta, turkey sauce, 1 cup mozzarella, 0.5 cup Parmesan, and the basil in the pot. Toss well.
Transfer mixture to a 9x13-inch baking dish. Mix breadcrumbs with remaining 1 tbsp olive oil. Sprinkle remaining mozzarella and 0.25 cup Parmesan over the casserole, then scatter the oiled breadcrumbs on top.
Bake 20–25 minutes until bubbly and golden. Broil 1–2 minutes to crisp the topping if desired. Rest 5 minutes before serving.