Layer half of the beef, mushrooms and onion in 3-1/2 to 4 qt crockpot; repeat layers. Pour soup over ingredients. Cover; cook LOW for 8 to 10 hours or until beef is tender and no longer pink.
1 1/4 lb beef round steak, 1 large onion, 1 can condensed French onion soup, 8 oz mushrooms
Before serving, toss stuffing mix and contents of seasoning packet with melted butter and 1/2 cup liquid from pot.
6 1/4 oz herb stuffing mix, 1/4 cup unsalted butter
Place stuffing on top of contents in crockpot; cover. Increase heat to high setting. Cook 10 minutes or until stuffing is fluffy. Sprinkle with cheese; cover. Cook until cheese is melted.