In a medium bowl, combine tuna, mayonnaise, celery, onion, relish, lemon juice, and garlic. Season to taste with salt and pepper (I like 1/2 teaspoon salt and 1/4 teaspoon pepper).
Arrange tortillas on a flat surface. Layer 2 slices of cheese, slightly overlapping, in the middle of each tortilla. Divide the tuna salad among them.
Top each tortilla with lettuce, about 3/4 cup tuna salad, sprouts (if using), and tomato slices. Wrap tightly in wax paper or plastic wrap and refrigerate until serving time. Slice in half to serve.
Notes
Tuna: Or, substitute oil-packed tuna (feel free to decrease the amount of mayonnaise if you do).
Mayonnaise: This recipe is heavy on the mayonnaise. Start with 1/4 cup if you prefer and add more to taste.
Sweet pickle relish: Or substitute dill relish or minced dill pickles.