01 - Preheat oven to 350°F. Grease a 9x13-inch baking pan.
02 - In a large bowl, combine cake mix, water, oil, and eggs. Beat with an electric mixer on medium speed for 2 minutes.
03 - Pour batter into prepared pan and bake for 28-32 minutes, or until a toothpick inserted in the center comes out clean.
04 - Cool cake in pan for 15 minutes.
05 - With the handle of a wooden spoon, poke holes all over the cake, spacing about 1 inch apart.
06 - In a medium bowl, dissolve lime gelatin in 1 cup boiling water. Add 1/2 cup cold water and stir well.
07 - Slowly pour the gelatin mixture evenly over the cake, letting it soak into the holes.
08 - Refrigerate cake for at least 2 hours, or until completely chilled and set.
09 - In a small bowl, fold lime zest and powdered sugar, if using, into whipped topping.
10 - Spread topping evenly over chilled cake. Garnish with extra lime zest.
11 - Slice and serve chilled.