Cut chicken breast into small, bite sized pieces. Heat a large stockpot over medium-high heat and add in 2 Tbsp. olive oil. Add chicken into the pot.
Season the chicken with salt and pepper. Cook the chicken cubes completely (until no longer pink). Set chicken aside on a plate.
Add last Tbsp. of olive oil and add in sliced mushrooms, onions and garlic and cook for 2-3 minutes on medium heat, stirring occasionally and then add chicken back in. Add in the chicken broth, heavy cream, marsala wine, pasta and seasonings.
Bring to a boil, then place lid on, turn heat down to low and cook for 10-12 minutes or until pasta is cooked. Remove lid. Mix cornstarch and milk in a small bowl and add into pasta to thicken. Bring to a boil to thicken for 5-10 min, adding more cornstarch as needed. Garnish with the fresh parmesan and parsley. Serve immediately.