01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish with cooking spray or olive oil.
02 - Bring a large pot of salted water to a boil. Add pasta and cook until just al dente, about 1-2 minutes less than package directions. Drain well and set aside.
03 - Heat a large skillet over medium heat. Add ground turkey and cook, breaking up with a spoon, until browned and cooked through, approximately 6-7 minutes.
04 - Add diced onion, minced garlic, and red bell pepper to the skillet with the turkey. Sauté for 4-5 minutes until vegetables are softened and fragrant.
05 - Stir in chopped baby spinach and cook for 1 minute until just wilted.
06 - Pour in marinara sauce, tomato paste, Italian seasoning, red pepper flakes, salt, and black pepper. Stir well to combine and simmer for 3-4 minutes to allow flavors to meld.
07 - Add cooked pasta to the skillet with the turkey sauce. Mix in half of the mozzarella and Parmesan cheeses, stirring until evenly distributed.
08 - Transfer the pasta mixture to the prepared baking dish, spreading evenly. Sprinkle the remaining mozzarella and Parmesan cheese over the top.
09 - Bake uncovered for 20-25 minutes, or until cheese is completely melted and beginning to bubble around the edges.
10 - Remove from oven and let rest for 5 minutes before serving. Garnish with fresh basil or parsley if desired.