Cut the chicken into bite-size pieces. Season with salt and pepper.
Heat a sauté pan to medium-high heat. Melt 2 tablespoons of butter. Add chicken and cook until browned, about 5 minutes.
Take the chicken out of the pan, and put it on a plate. Add the tablespoon of butter to the pan, then add onions and mushrooms. Cook until soft and brown, about 10 minutes.
Add the garlic and cook for another minute.
Add the chicken back to the pan.
Add Marsala, cream, and chicken stock. Bring to a simmer and let it thicken, approximately 10 minutes.
While the sauce is simmering, in a separate pot, bring water to a boil to cook the pasta.
Cook the pasta to al dente per package instructions. Reserve about 2 tablespoons of the pasta water.
Mix the pasta into the Marsala sauce with the reserved pasta water and the Parmesan.
Add parsley and serve.