1) Stir the gelatin in hot water to dissolve.
2) Then stir in the lemon juice, mayonnaise, salt and cold water.
3) In a freezing tray, pour the mixture and freeze for about 15-20 minutes, or until set towards the edges but soft in the center.
4) In a bowl, remove the mixture and whip until fluffy with a rotary beater.
5) Then fold in the chopped green pepper and grapefruit sections.
6) In a 1-quart mold, pour the mixture and refrigerate for 30-60 minutes, until set.
7) Unmold in a platter and serve immediately.