1. Drain and flake tuna. Add mayonnaise, ketchup, salt, cayenne pepper, onion and Worcestershire sauce.
2. Pare cucumber and slice paper-thin (if desired, sprinkle with paprika).
3. For each canape, place cucumber slice on toast round, pile tuna mixture in center and top with olive slice.
4. Put 8 canapes in circle on individual paper plates. For each plate, cook uncovered in microwave oven 30 to 60 seconds.