1. Sprinkle gelatin over cold water in medium bowl; let stand for 5 minutes to soften. Add boiling water; stir until gelatin is completely dissolved.
2. Stir in frozen lemonade concentrate, undrained pineapple chunks and lemon or lime juice. Pour into 4-cup mold; chill until completely set, about 2 hours. Dip mold into hot water and invert onto serving platter; shake to release mold.