Saute bacon, mushrooms & onions until soft. Add cheese. Cook until melted. Remove. Spread mushroom mixture evenly on bread slices. Roll up. Secure with toothpicks. Place seam side down on bake trays. Chill and cover for 1 hour or freeze in single layer. Brush rolls with melted butter. Bake in a moderate to hot oven for 10 – 12 minutes.