Heat the mashed potatoes for 3 minutes. Stir in half cup of the Chef's Blend cheese and set aside. Spray a large skillet with cooking spray. Add the steak, and mushrooms; cook at medium high heat for 1 minute. Cut any large piece of steak to bite size pieces. Add the Marsala wine and continue to cook on medium high heat until most of wine is absorbed, approximately 12 minutes. Do not cook all wine out, leave about half a cup of juices. Remove from heat. Layer half of steak and mushrooms, then half of the potatoes and half of the remaining cheese in a prepared 2 quart souffle baking dish. Repeat layers. Bake at 350 degrees for approximately 25 to 30 minutes or until desired browness of cheese.