Spray a 12-inch pizza pan with cooking spray: set aside. Heat butter in a large sauce pan over medium heat. Stir in marshmallows until marshmallows are melted. Stir in popcorn until well coated. Spread mixture evenly onto prepared pizza pan. Drizzle red piping gel over "pizza" for "sauce." Cut small circles (about 1.5 inch diameter) from fruit roll-up and place on pizza for "pepperoni" slices. Decorate as desired with jelly beans, coconut and candies. Allow to cool completely before cutting into wedges to serve.