Bring a pot of water to a boil and cook spaghetti according to package instructions. Drain and set aside.
In a large skillet over medium heat, add butter and onions. Cook until tender. Add ground turkey and minced garlic and cook, breaking up turkey with a spatula. Cook until turkey is cooked through completely.
Sprinkle flour and seasonings into turkey mixture and stir to combine. Slowly stir in half and half and chicken broth until combined. Continue to cook until sauce lightly thickens. Stir in parmesan cheese.
Stir spaghetti into your sauce and gently mix until well combined. Serve with fresh grated parmesan cheese and red pepper flakes.