01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly with cooking spray or butter.
02 - Combine white cake mix, water, vegetable oil, and eggs in a large bowl. Beat on medium speed for 2 minutes until batter is completely smooth and well incorporated.
03 - Pour batter into prepared pan and bake for 28-32 minutes. Cake is done when a toothpick inserted into the center comes out clean.
04 - Remove cake from oven and let cool for 15 minutes. Using the handle of a wooden spoon, poke holes evenly across the entire cake surface, spacing approximately 1 inch apart.
05 - Dissolve lime gelatin in 1 cup boiling water, stirring until completely dissolved. Stir in 1/2 cup cold water and mix well.
06 - Slowly pour the gelatin mixture over the warm cake, ensuring the liquid fills all the poked holes evenly across the surface.
07 - Refrigerate the cake for at least 2 hours to allow the gelatin to completely set and the cake to cool thoroughly.
08 - Spread thawed whipped topping evenly over the entire surface of the chilled cake using an offset spatula or knife.
09 - Sprinkle fresh lime zest over the whipped topping. Add green sprinkles or fresh lime slices if desired. Cut into squares and serve cold.