Heat oven to 350°F (325°F for dark or nonstick pan). Spray bottom only of 13x9-inch pan with baking spray with flour. In small bowl, mix hot water and gelatin until gelatin is completely dissolved; cool slightly.
2 In large bowl, beat cake mix, 1/4 cup of the gelatin mixture, 1/4 cup of the lemonade concentrate, the water, oil, and egg whites with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes. Pour into pan. Reserve remaining gelatin mixture and lemonade concentrate.
3 Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Poke warm cake every inch with fork tines. Remove 1 tablespoon of the reserved gelatin mixture to microwavable custard cup or small bowl. In another small bowl, mix remaining gelatin mixture and remaining 1/4 cup lemonade concentrate; pour slowly over cake. Cool completely, about 1 hour.
4 In medium bowl, fold together frosting and whipped topping; frost cake. Microwave 1 tablespoon gelatin mixture uncovered on High 10 seconds to liquefy. Using 1/4 teaspoon measuring spoon, place small drops of gelatin mixture over frosting; with spoon or toothpick, swirl gelatin into frosting. Garnish each piece with raspberries and lemon peel strips. Store covered in refrigerator.