In a medium bowl whisk together mayonnaise, mustard, curry powder, salt, and pepper. Mix in tuna, shallot, apple, walnuts, celery, and pickle relish. Mix until all the ingredients are coated with the dressing.
Place a lettuce leaf on the bottom half of a slice of Rye bread. Add a layer of tuna salad on top of the lettuce and top with a slice of Swiss and the top half of the rye bread. Repeat until all sandwiches are made.