Bake Lemon Cake according to package for 13x9-inch pan. Cool cake in pan 15 min. Pierce cake with large fork at 1/2-inch intervals.
Add boiling water to gelatin mix in small bowl; stir 2 min. until completely dissolved. Stir in cold water; pour over cake. Spread Lemon curd over the cake evenly, allowing it to go down into the holes as well. Refrigerate for atleast 3 hours.
FROST cake with COOL WHIP. Refrigerate until ready to serve.