01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Cook pasta in a large pot of salted boiling water until just al dente. Drain and set aside.
03 - In a large skillet over medium heat, cook ground turkey until browned and cooked through, about 6-7 minutes. Break up meat with a spoon.
04 - Add diced onion, garlic, and red bell pepper to the turkey; sauté for 4-5 minutes until softened.
05 - Stir in chopped spinach and cook for 1 minute until wilted.
06 - Add marinara sauce, tomato paste, Italian seasoning, red pepper flakes, salt, and black pepper. Simmer for 3-4 minutes.
07 - Combine cooked pasta with turkey sauce in the skillet or a large bowl. Mix in half of the mozzarella and Parmesan.
08 - Transfer mixture to prepared baking dish. Sprinkle remaining mozzarella and Parmesan over the top.
09 - Bake uncovered for 20-25 minutes, until cheese is melted and bubbly.
10 - Let rest for 5 minutes before garnishing with fresh basil or parsley and serving.