STIR boiling water into dry gelatin mix in large bowl at least 2 min. until completely dissolved. Add seltzer, lemon peel and juice; stir until well blended. Pour into 8-inch square pan; cover. Freeze 3 hours or until firm.
REMOVE mixture from freezer; let stand at room temperature 10 min. to soften slightly. Spoon into large bowl. Beat with electric mixer on medium speed until smooth. (Or, place in a food processor container; cover and process until smooth.)
SPOON or scoop gelatin mixture into six individual dessert dishes to serve.