Mix 3 packages Knox gelatin with 2/3 cup warm water. Whip 2 packages Dream Whip or use Cool Whip and add to gelatin mixture. Stir well. Add 2 cans crushed pineapple (in own juice) and 2 teaspoons lemon juice. Let set in refrigerator for 5 minutes. Pinch up angel food cake into 9 x 12 inch pan. Stir in mixture and set in refrigerator overnight. Cover with Cool Whip. Coconut may be sprinkled on top, if desired.