Preheat the broiler and position the oven rack about 6 inches from the broiler.

Combine the tuna, olives, mayonnaise, red onion, capers, black pepper, lemon juice, and salt in a medium bowl. Stir until well mixed.

Arrange the bread slices on a work surface. Lightly spread each slice of bread with additional mayonnaise and top with 2 tomato slices each. Divide the tuna salad evenly among the 4 bread slices over the tomatoes. Top the tuna salad with slices of provolone.

Place sandwiches on a sheet tray and place under broiler. Cook until cheese is golden and bubbly, about 5 minutes.