¼ cup finely diced red onion
¼ cup extra virgin olive oil
1 Tbsp balsamic vinegar
1 Tbsp minced basil
½ tsp crushed red pepper
salt and freshly ground black pepper
4 ciabatta rolls, split
Dijon mustard and mayonnaise, for spreading
8 1/4-inch-thick slices of Swiss or cheddar cheese, 6 ounce
16 1/8-inch-thick lengthwise slices of kosher dill pickle
2 Tbsp unsalted butter, softened
1. In a medium bowl, mix the tuna with the onion, olive oil, vinegar, basil and crushed red pepper. Season with salt and pepper.
2. Heat a panini press or griddle. Spread the cut sides of the rolls with mustard and mayonnaise and top each roll half with a slice of cheese. Spread the tuna salad on the bottoms and cover with the pickles. Close the sandwiches and spread the outsides of the rolls with the butter.
3. Add the sandwiches to the press and cook over moderate heat until the cheese is melted, about 6 minutes. Cut the sandwiches in half and serve.