Preheat your oven to 350°F (175°C) to prepare for baking.
In a large pot, bring water to a boil and cook the spaghetti according to package directions until al dente. Once cooked, drain the spaghetti and set it aside.
While the pasta cooks, heat the olive oil in a large skillet over medium heat. Once hot, add the diced onion and sauté until it becomes translucent, about 3-4 minutes.
Add the minced garlic and diced bell pepper to the skillet, stirring and cooking for an additional 2-3 minutes until the vegetables are slightly softened.
Introduce the ground chicken or turkey to the skillet, using a wooden spoon to break it apart. Cook until it is browned and no longer pink, approximately 5-7 minutes.
Mix in the drained diced tomatoes, Italian seasoning, and optional red pepper flakes. Season generously with salt and freshly cracked black pepper. Cook for an extra 2-3 minutes to blend the flavors.
In a large mixing bowl, combine the cooked spaghetti with the heavy cream, half of the shredded cheddar cheese, and half of the shredded mozzarella cheese. Toss well to ensure even coating.
Gently fold the sautéed meat and vegetable mixture into the spaghetti mixture, ensuring it is evenly distributed throughout.
Pour the combined spaghetti mixture into a well-greased 9x13 inch baking dish, spreading it out evenly.
Sprinkle the remaining cheddar and mozzarella cheeses generously over the top for a cheesy finish.
Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the cheese is beautifully melted and bubbling.
Once baked, carefully remove from the oven and allow it to cool slightly for about 5 minutes before serving.
Notes
Serve hot, garnished with fresh parsley and a drizzle of extra heavy cream for an elegant touch.