Bring a large pot of salted water to a boil. Add pasta and cook until al dente, about 8–10 minutes. Reserve 1 cup of pasta water, drain the pasta, and set aside.

In a large skillet, melt butter over medium heat. Add diced chicken breast, season with salt and pepper. Cook for 6–8 minutes until golden brown. Remove chicken, keeping juices in the pan.

In the same skillet, melt remaining butter. Add minced garlic and diced onion. Sauté until onion is translucent, about 3–4 minutes.

Pour in heavy cream and chicken broth, stirring to combine. Add Italian seasoning and red pepper flakes. Simmer for 5 minutes until thickened.

Return chicken and drained pasta to the skillet, toss to coat in sauce. Cook for an additional 2 minutes.

Serve warm, topped with Parmesan cheese and chopped parsley.