Prepare a 10 by 15 inch jelly roll pan by lining with with aluminum foil and spraying it with cooking spray.
Melt the butter in a large pot over medium heat.
Add the marshmallows and stir until they are completely melted. Stir in the green food coloring.
Remove the pot from the heat and stir in the Rice Krispies.
Pour the mixture into the prepared pan. Using a piece of wax paper that was sprayed with cooking spray, press the mixture firmly into the pan.
Allow it to cool completely. Lift the foil from the pan, cut it in half as shown above, then cut into triangle pieces.
Spread one triangle with vanilla buttercream frosting. Place a straw in the middle of it and top with another triangle pressing down firmly. Decorate with more frosting and sprinkles.
Store in an airtight container for up to three days.