The chicken breast turns out tender and flavorful in the cheesy and creamy mushroom and onion sauce. The onions are optional, but highly recommended :)!
Meanwhile, sauté the sliced mushrooms until all liquid evaporates. Add the sliced onion and sauté until the onions and mushrooms have slightly browned. Sprinkle with a pinch of salt and stir in sour cream and shredded cheese. Allow sauce to thicken.