Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Drain and set aside.

In a skillet over medium heat, add the ground turkey. Cook until browned, breaking it apart with a wooden spoon, about 5-7 minutes.

Add the chopped onion, garlic, and bell pepper to the skillet. Sauté until the vegetables are soft, about 3-4 minutes.

Stir in the diced tomatoes, tomato paste, Italian seasoning, salt, and black pepper. Simmer for 5-7 minutes until the sauce thickens slightly.

Add the chopped spinach and cook until wilted, about 2 minutes.

Add the cooked pasta to the skillet and toss to combine with the sauce. Cook for an additional 2 minutes to heat through.

Serve hot, garnished with grated Parmesan cheese if desired.