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 completely smooth and well blended.
03 - Pour batter into prepared pan. Bake for 28-32 minutes or until a toothpick inserted in center emerges clean.
04 - Remove cake from oven and let cool for 15 minutes. Use wooden spoon handle to poke holes across surface, spacing 1 inch apart.
05 - Dissolve lime gelatin in boiling water, stirring until completely dissolved. Mix in cold water.
06 - Slowly pour gelatin mixture evenly over cake, ensuring liquid penetrates the poked holes.
07 - Refrigerate for at least 2 hours until gelatin is fully set and cake is thoroughly chilled.
08 - Spread whipped topping evenly over the entire surface of the chilled cake.
09 - Sprinkle with fresh lime zest and add green sprinkles or lime slices if desired. Cut into squares and serve cold.