Preheat oven to 325ºF. Prepare a jelly roll pan with shortening and flour or a non-stick cooking spray. Set aside for later.
Prepare the cake mix according to the directions on the box.
Transfer the batter into 2 Ziplock bags or a prepared piping bag. Cut a small corner off of each Ziplock bag. Squeeze stripes of each color In a diagonal pattern, until the pan is filled, alternating between green and red.