Combine the olives, garlic and capers in an electric food processor, and process to form a paste. With the motor still running, slowly add the olive oil through the feed tube and blend thoroughly. Then add the tuna, lemon juice, pepper and pulse until blended but still chunky. Then take out of the food processor and mix with the chopped tomatoes and cucumber. Scoop out portions of this mixture onto lettuce leaves and wrap em up :).