The Perfect Tuna Melt

Name: The Perfect Tuna Melt
Cuisine: American
Ingredients: Tuna (2 x 5oz cans, drained); Onion (medium size, chopped); Celery (1/2 a stalk, chopped); Garlic (1 clove, minced); Parsley (1 tablespoon, chopped); Mayonnaise (3-4 tablespoons); Extra Virgin Olive Oil (3 tablespoons, divided); Mozzarella (1/3 cup, shredded); Bread (sliced); Butter (softened); Salt and Pepper to taste