Preheat oven to 350 degrees F. Spray a 9×13 baking dish with cooking spray and set aside. Heat olive oil in a skillet over medium-high heat. Add the chicken breasts, cover pan, and cook for 3 minutes on each side (salt and pepper each side).
Transfer the chicken to the prepared baking dish. Add the butter to the skillet (do not clean out remnants) and decrease heat to medium. Add the garlic, mushrooms, onion, parsley, salt and pepper and cook, stirring, until soft and fragrant, about 3 minutes. Add the flour and stir until mixture is thick. Add the broth and cream and bring to a boil over medium-high heat.
Remove pan from heat and pour the mixture over the chicken in the baking dish. Top with the Parmesan cheese and extra parsley. Bake in the preheated oven for 15-20 minutes, or until the chicken is cooked through. Serve warm with rice, quinoa or pasta!