In a small mixing bowl break up the tuna with a fork. Toss with celery, onion, 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.
Assemble the sandwich: Layer the bread with lettuce, tomato, and tuna salad. Top with a slice of bread then cut in half.
Prepare the pineapple orange spritzer: In a mixing jug or bowl, combine the pineapple juice and orange juice. Pour the fruit juice mixture evenly into glasses over ice.
Top each glass with sparkling water or club soda. Stir.
Serve: Enjoy the sandwich with barbecue chips, pickle, and pineapple orange spritzer.