01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan thoroughly with cooking spray or butter.
02 - Combine cake mix, water, vegetable oil, and eggs in a large bowl. Beat according to package directions until smooth, approximately 2 minutes. Pour batter evenly into prepared pan.
03 - Bake for 28-32 minutes until a toothpick inserted in the center comes out clean. Remove from oven and allow to cool in pan for 15 minutes.
04 - Using the handle of a wooden spoon, poke holes evenly across the entire surface of the cake, spacing approximately 1 inch apart.
05 - Dissolve lime gelatin completely in 1 cup boiling water, stirring until no granules remain. Stir in 1/2 cup cold water.
06 - Slowly pour the gelatin mixture over the warm cake, ensuring liquid seeps into the poked holes evenly across the surface.
07 - Refrigerate cake for at least 1 hour until completely chilled and gelatin is fully set.
08 - In a chilled bowl, beat heavy cream, powdered sugar, and vanilla extract with electric mixer until stiff peaks form, approximately 3-4 minutes.
09 - Spread whipped cream evenly over the chilled cake. Sprinkle with fresh lime zest. Optional: arrange thin lime slices on top for decoration.
10 - Slice into 12 equal portions and serve immediately, or keep refrigerated until serving time.