01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - Combine cake mix, water, vegetable oil, and eggs in a large bowl. Beat according to package directions until smooth and well incorporated. Pour batter into prepared pan, spreading evenly.
03 - Bake for 28-32 minutes until a toothpick inserted in the center comes out clean. Remove from oven and allow to cool for 15 minutes.
04 - 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.
06 - Slowly pour the gelatin mixture over the warm cake, ensuring it seeps into the poked holes evenly across the surface.
07 - Refrigerate for at least 1 hour or until completely chilled and gelatin is fully set.
08 - In a chilled bowl, beat heavy cream with powdered sugar and vanilla extract until stiff peaks form. For convenience, substitute with 8 oz pre-made whipped topping.
09 - Spread whipped cream evenly over the chilled cake. Garnish with fresh lime zest and optional thin lime slices.
10 - Slice into squares and serve chilled for best texture and flavor.