In large, heavy saucepan, sauté the garlic in the oil, over medium heat, for few minutes.
Add sausages, stock and water, tomatoes, celery, onions, carrots and lentils. Bring mixture to a boil, then reduce heat, cover the pan and simmer the soup for 1-1 1/2 hours, or until lentils are tender.
Salt and pepper to taste. You cna also sprinkle some grated parmesan cheese on top