First pick over lentils; remove any pebbles or twigs; set aside.
Next, dice the carrots, celery and potatoes; cover with water in a bowl and set aside.
Saute the onion in the soup pot until softened, but not browned, either in oil, or a little tomato juice from the can of tomatoes.
Add the diced carrots, celery, potatoes and water.
Add the barley,pureed tomatoes and lentils; add salt,pepper and parsley.
Add 2 quarts of water and the onion soup.
Bring to a boil; turn heat down and simmer 1 hour. Add more water if needed. Stir occasionally.
Soup is done when the barley is tender.