Remove top from can of sliced pineapple completely. Drain. Leave slices in can. Heat pineapple juice, mix with gelatin. Stir until dissolved. Cool, pour back into can. Let set a while, then use fork and lift slices of pineapple to allow gelatin mixture to get in between slices.

Place can in refrigerator. Allow to set overnight. When ready to serve, remove other end of can. Shake salad out of can. Slice with knife between slices of pineapple. Serve on lettuce with mayonnaise.