Preparation

Place tuna and shrimp in a shallow, nonmetallic dish; set aside. Combine lemon juice and next 3 ingredients; pour over seafood and stir gently. Cover and refrigerate 1 hour. Drain, discarding marinade. Thread 3 shrimp and 2 tuna cubes alternately onto eight 6 inch skewers. Coat grill rack with vegetable cooking spray. Place kabobs on grill 4 to 5 inches from medium hot coals. Grill, turning once, just until shrimp is opaque and tuna begins to flake when tested with a fork, allowing about 3 minutes on each side. Arrange bread slices on individual serving plates. Spread teaspoons Lemon Caper Mayonnaise on each slice. Top each with a lettuce leaf and 2 tomato slices. Place 2 kabobs on each sandwich and carefully remove skewers. Top with remaining mayonnaise.