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 of celery and carrot into sticks and eat with sandwich.