Preheat oven to 180ºC. Grease 2 x 23cm round cake pans with butter; sprinkle lightly with flour.
Beat cake mix, egg whites, oil and mango juice in large bowl with electric mixer on low speed until moistened. Beat on medium speed for 2 minutes. Fold in 2 teaspoons of lime zest . Divide the mixture evenly between the cake pans.
Bake 20 to 25 minutes until golden and toothpick inserted in center of cakes come out clean. Cool 10 minutes. Run knife around sides of pans to loosen cakes; remove from pans to cooling rack. Cool completely.
Beat whipping cream mix and cold milk in medium bowl as directed on package.
Place one cake on a serving plate. Spread with 2/3 of the whipping cream; top with 2/3 of the chopped mango and half the coconut. Top with the second cake. Spread remaining whipping cream in the center; top with remaining chopped mango, coconut and lime zest. Store loosely covered in the refrigerator.