Begin by draining the two cans of tuna and transferring the contents to a mixing bowl. Next, chop the onion, celery, and parsley, and mince the garlic. Add all these ingredients to the bowl with the tuna. Mix well until evenly combined.

Stir in 3-4 tablespoons of mayonnaise and 3 tablespoons of extra virgin olive oil. Mix in the 1/3 cup of shredded mozzarella cheese. Season your mixture with salt and pepper to taste.

Place a non-stick skillet over medium heat and add 1 tablespoon of olive oil. Allow the oil to heat up for about one minute.

Take a slice of bread and butter one side generously. Place the buttered side down into the skillet. Spoon about 2 tablespoons of the prepared tuna mixture onto the bread.

Butter another slice of bread on one side. Once your first slice with the tuna mixture has heated for about 2-3 minutes and is golden brown, place the second slice, butter-side up, on top of the mixture.

Cook the sandwich for an additional 2-3 minutes or until the bottom slice is golden brown. Carefully flip the sandwich using a spatula; cook the other side for another 2-3 minutes.

Once both sides of your Tuna Melt are perfectly toasted, remove it from the skillet. Let it rest for a minute before slicing it in half.