Cook bacon, mushrooms and onion until tender but not crispy. Mix with cream cheese. Trim crust off bread and roll slices flat. Spread 2 tbsp of cream cheese mixture on each slice and roll up, securing with a toothpick. Place rolls seam-side down on baking sheet. Cover and chill at least one hour. Brush with melted butter and bake at 375°F for 10-15 minutes or until rolls are toasty brown. Remove from oven, take out toothpicks and cut each roll in half.