In a large bowl, gently combine eggs with tomato, olives, capers, tuna, potatoes, chives, tarragon and basil. For the dressing: in a small bowl, combine mayonnaise with mustard, anchovy paste and pepper. Gently stir in egg mixture. Add salt to taste, if necessary. Divide egg mixture between 4 slices of bread; spread evenly. Top with lettuce leaves and 4 remaining slices of bread. Cut each sandwich in half diagonally.