Preheat Your Oven: Follow the instructions on your cake mix box for preheating.
Prepare the Cake Mix: In a large bowl, combine the cake mix with the required eggs and oil. Replace the water with Orange Crush soda. Mix until smooth.
Bake the Cake: Pour the batter into a greased 9×13 inch baking pan. Bake according to the package directions, or until a toothpick inserted into the center comes out clean.
Poke the Cake: Once baked, remove the cake from the oven. While still warm, use the end of a wooden spoon to poke holes all over the top of the cake.
Prepare the Pudding Mixture: In a medium bowl, whisk together the instant vanilla pudding mix, milk, and orange zest until smooth and slightly thickened.
Fill the Holes: Pour the pudding mixture over the warm cake, aiming to fill the holes created.
Cool and Top: Allow the cake to cool completely. Then, spread the whipped topping evenly over the top.
Garnish and Refrigerate: Garnish with orange slices or additional zest if desired. Refrigerate for at least 1 hour before serving to allow the cake to absorb the flavors and firm up.