Preheat oven to 350 degrees F. Grease and flour a 9-inch x 13-inch baking dish. Set aside.
Prepare cake mix with water, vegetable oil, and egg whites according to package directions.
Bake at 350 degrees for 29-33 minutes. Let cake cool to room temperature. After the cake has cooled, poke holes into the cake with a fork.
Boil 1 cup of water; remove from heat. Add in gelatin mix and stir about 2 minutes or until well dissolved. Add 1/2 cup of cold water and stir to combine.
Pour the Jell-O into the holes that were poked into the top of the cake, being sure to pour all the Jell-O over the cake. Refrigerate the cake for at least 3 hours to let the Jell-O setup.
Once chilled, top the cake with the whipped topping. Add the sliced strawberries for garnish. Slice and serve the cake. Cover and refrigerate any leftovers.