Cook pasta in a large pot of salted boiling water according to package instructions for 8–10 minutes until al dente. Reserve 1 cup pasta water, drain, and set aside.

In a large skillet, melt 2 tablespoons of butter over medium heat. Cook seasoned diced chicken for 6–8 minutes until golden brown and cooked through, then set aside.

Add remaining butter to the skillet. Sauté minced garlic and chopped onion for 3–4 minutes until onion is translucent.

Pour in heavy cream and chicken broth, stirring in Italian seasoning and red pepper flakes. Let simmer for 5 minutes, adding reserved pasta water if needed.

Combine cooked chicken and drained pasta into the sauce, tossing gently. Heat through for 2 minutes.

Serve hot, topped with Parmesan cheese and parsley.