In a medium mixing bowl stir together the tuna or salmon, egg, tomato, olives, onion, and, if desired, capers. Set aside.
For dressing, in a small mixing bowl stir together the mayonnaise or salad dressing, lemon juice, garlic, and pepper. Stir dressing into the tuna or salmon mixture.
To serve, cut the pita bread rounds in half crosswise, forming 4 pockets. Line each pocket with lettuce leaves. Spoon about 1/3 cup of the tuna or salmon mixture into each pita pocket. To serve, if desired, cut the pockets in half, forming 8 triangles. Makes 2 servings.
Tummy-warming cheese soup goes well with these hearty sandwiches.