2) In a large bowl combine the anchovy paste and olive oil. Add the olives, onions, celery, tuna, lemon juice and pepper, to taste, and toss to combine.
3) Lightly butter each side of the rolls and toast on each side under the grill. Fill the rolls with the tuna salad and top with cheese. Arrange on a baking tray and grill until the cheese melts. Transfer to serving plates and serve.