Add the tuna to a small mixing bowl, and break up with a fork. Toss with celery, vinegar, and mayonnaise, as needed until the tuna, is to your desired creaminess. Season with salt and pepper to taste. Stir to combine.
Lightly toast the bread. Top with lettuce, tuna salad, onion, and tomatoes.
Serve: Cut in half and enjoy with chips and pickle spears. Enjoy with sparkling water.