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 boiling water and gelatin until gelatin is completely dissolved. Cool slightly, about 5 minutes.
In large bowl, beat cake mix, 1/4 cup of the gelatin mixture, 1/4 cup of the orange juice concentrate, the oil, water and egg whites with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan. Reserve remaining gelatin mixture and orange juice concentrate.
Bake 25 to 30 minutes or until toothpick inserted in center comes out clean. Poke warm cake every inch with fork. Place 1 tablespoon of the reserved gelatin mixture in small microwavable bowl; set aside. Into remaining gelatin mixture, stir remaining 1/2 cup orange juice concentrate; pour slowly over cake. Cool cake completely, about 1 hour.
In medium bowl, gently stir 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 cake piece with orange peel strips. Store covered in refrigerator.