When company comes and the budget will allow it, substitute shrimp or crabmeat for the tuna.
Soften the gelatin in cold water. Heat the soup to boiling and add the gelatin, stirring to dissolve. Stir in the mayonnaise, lemon juice and mustard. Chill until partially set; fold in the tuna, celery, cucumber and green pepper. Turn into an 8-½x4-½x2-½-inch loaf pan. Chill until firm.
To serve, slice and place on shredded lettuce. Garnish with pitted ripe olives.