Directions:

In medium saucepan, combine lentils and water. Bring to a boil. Reduce heat; cover and simmer for 10 minutes.

In a 3 to 4 quart slow cooker, combine celery, carrots, onion, ketchup, brown sugar, Worcestershire sauce and lentils with water; mix well. Cover and cook on low setting for 10 to 12 hours.

Just before serving, stir in vinegar. Spoon 1/2 cup filling onto each bun.