Prepare cake mix as directed on pkg. Bake in 13 x 9 inch pan. (this is where adult supervision may be necessary) Cool cake in pan 15 minutes; then prick with utility fork at 1/2 inch intervals. Meanwhile, dissolve jello in hot water. Add cold water and carefully pour over warm cake. Chill 3 to 4 hours in frig. Top with Cool Whip. Cut into squares. Garnish with strawberries if desired. Keep in refrigerator.