01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly.
02 - Combine cake mix, water, oil, and eggs according to package directions. Pour batter into prepared pan and bake for 28-32 minutes until a toothpick inserted in the center comes out clean.
03 - Remove cake from oven and let cool for 10 minutes. Using the handle of a wooden spoon, poke holes evenly across the entire cake surface, spacing about 1 inch apart.
04 - Dissolve lime gelatin completely in boiling water. Stir in cold water and mix until well combined.
05 - Slowly pour the gelatin mixture evenly over the warm cake, ensuring it seeps into the poke holes for maximum absorption.
06 - Refrigerate the cake for at least 1 hour to allow the gelatin to set completely.
07 - Beat heavy cream with powdered sugar and vanilla extract until stiff peaks form. Alternatively, use prepared whipped topping.
08 - Spread whipped topping evenly over the chilled cake. Garnish with fresh lime zest and optional lime slices. Keep refrigerated until ready to serve.