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