Mash beans with a bean masher. Place in a bowl and add celery, onions, relish, lemon juice and fat-free tofu mayonnaise. Mix well. Chill to blend flavors. Spread bread with mustard, if desired. Place about 1/2 cup of the spread on four of the bread slices. Add lettuce, tomatoes if desired, close up and eat. Cut up a celery and carrot into sticks and eat with sandwich.