Bring a large pot of salted water to a boil. Cook the pasta according to package instructions until al dente. Drain and set aside.
In a large skillet or pot, heat olive oil over medium-high heat. Add the diced onion, green bell pepper, and red bell pepper. Sauté for 3–4 minutes until softened and fragrant.
Add the ground turkey to the skillet. Break it apart with a spoon and cook for 6–7 minutes, or until fully browned and cooked through.
Stir in crushed tomatoes, tomato sauce, and tomato paste. Add the minced garlic, oregano, basil, sea salt, black pepper, and red pepper flakes (if using). Mix well to combine.
Reduce heat to medium-low and let the sauce simmer for about 30 minutes, stirring occasionally, until thickened and flavorful.
Add the cooked pasta to the sauce and toss until evenly coated. Let it cook together for 2–3 minutes to heat through. Remove from heat and allow to rest for 10 minutes before serving.
Plate the turkey spaghetti and garnish with grated Parmesan cheese or fresh herbs if desired.