Beat cake mix, dry pudding mix, water, egg whites, and oil in a large bowl with electric mixer on low speed until moistened. Batter will be thick. Beat on medium speed 2 minutes. Spoon batter evenly into 24 paperlined muffin cups.
Bake 21-24 minutes or until toothpick comes out clean. Cool in pans 10 minutes, remove to wire racks and cool completely.
Beat sugar, cream cheese, butter, and juice with electric mixer on low speed until well blended, frost cupcakes.
Stir 1 tsp grated lemon peel into frosting mixture. Garnish with additional grated lemon peel.