01 - Preheat oven to 350°F. Generously grease a 9x13-inch baking pan with cooking spray or butter.
02 - Combine cake mix, water, vegetable oil, and eggs in a large bowl. Beat on medium speed for 2 minutes until batter is smooth and well-combined.
03 - Pour batter into prepared pan and bake for 28-32 minutes until toothpick inserted in center comes out clean.
04 - Remove from oven and let cake cool for 15 minutes. Using wooden spoon handle, poke holes evenly across surface at 1-inch intervals.
05 - Dissolve lime gelatin in boiling water, stirring until completely dissolved. Stir in cold water.
06 - Slowly pour gelatin mixture over cake, ensuring liquid fills all holes evenly.
07 - Refrigerate for at least 2 hours until gelatin is completely set.
08 - Spread whipped topping evenly over chilled surface.
09 - Sprinkle lime zest over top. Add green sprinkles or lime slices if desired. Cut into squares and serve cold.