This salsbury steak leftovers for lunch is comfort food at its best. Just fry up some sliced mushrooms in butter then add to bowl. In another bowl, add a third can of French onion soup, One egg, 1# ground beef, 1/2 c bread crumbs and salt and pepper and mix with your hands to form 4 patties and brown in pan. In mushroom bowl, add rest of soup, squirt of ketchup, splash of worchestershire, 1/3 c water, 1T flour, 1Tdry mustard and mix. Flip burgers and add sauce and cover and cook on low for 20min.