This is a simple soup, delicious and bursting with nutrition. It can be made a day or two in advance, leaving out the pasta and Swiss chard. Just before re-heating the soup, add them in, so they retain their bite and colour.
Wash and pick over the lentils, and put them in a large soup pot with the water and bay leaves. Bring them to a boil, then reduce to a simmer.
Prepare the onions, celery and carrots, and sauté them in the olive oil until soft and slightly browned in spots. Add them to the lentils when the lentils are getting tender; after about 30 minutes of cooking.
Dissolve the tomato paste in some of the soup water, and mix it into the soup. Add the salt, pepper and oregano.
Cook the pasta in plenty of salted, boiling water until almost tender. Drain and add to the soup.
Wash the Swiss chard well, and shred it finely. Add it to the soup, and simmer until the pasta is tender and the chard is bright green.
If soup appears to be too dry at this time, add more liquid. (This should be a thick, stew-like soup, but, if heat is too high, there may be too much evaporation).
When the soup is fully cooked, stir in 2-3 tablespoons lemon juice, or to taste.