Spay 12-inch pizza pan with cooking spray; set aside. In large saucepan over medium heat, heat butter. Stir in marshmallows until melted, then stir in popcorn until coated. 

Spread mixtures evenly onto prepared pizza pan. Drizzle red piping gel over the "pizza" to make the "sauce." 

Cut small circles (about 1 1/4 inches in 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 slices to serve.