In a small bowl, break up the tuna with a fork. Toss with celery, lemon juice, and mayonnaise as needed until the tuna is to your desired creaminess. Season with pepper to taste. Stir to combine.
Lightly toast the bread in a toaster oven.
Top the toasted bread with the Tuna Salad, onion, lettuce, and tomatoes.
Cut in half. Serve with carrot sticks, ranch, and apple juice.