Emeril's Kicked-Up Tuna Melts

INGREDIENTS

• 4 cans (5 ounces each) solid white tuna packed in water, drained
• 1/3 cup mayonnaise, plus more for spreading
• 1/4 cup finely chopped red onion
• 4 teaspoons capers, rinsed and drained
• 1 tablespoon fresh lemon juice
• 1/2 teaspoon coarse salt
• 1 teaspoon ground pepper
• 1/4 teaspoon dried oregano, crumbled between your fingers
• 4 slices crusty bread
• 8 thin slices tomato
• 4 slices provolone