Oregon Tuna Melts

Name: Oregon Tuna Melts
Ingredients: Two 6-ounce cans albacore tuna; 1/4 cup finely diced red onion; 1/4 cup extra-virgin olive oil; 1 tablespoon balsamic vinegar; 1 tablespoon minced basil; 1/2 teaspoon crushed red pepper; Salt and freshly ground pepper; 4 ciabatta rolls, split; Dijon mustard and mayonnaise, for spreading; Eight 1/4-inch-thick slices of Swiss or cheddar cheese (6 ounces); Sixteen 1/8-inch-thick lengthwise slices of kosher dill pickle; 2 tablespoons unsalted butter, softened