In a small mixing bowl break up the tuna with a fork. Toss with celery, onion, lemon juice, and mayonnaise. Season with pepper to taste. Stir to combine.
Lightly toast the bread, top with the Tuna Salad, tomatoes, and cheese. Place on a baking sheet under the broiler and cook until the cheese has melted.
Serve with chips and pickle. Garnish with parsley.