Heat the oil in a large pot over medium heat. Add the onions and cook until they're translucent, 5 to 6 minutes. Add the carrots and celery and cook for a few more minutes.

Add the lentils, water, thyme and bay leaf. Simmer, stirring occasionally, until the lentils are soft and the soup has thickened, 1 to 1 1/2 hours.

Add salt to taste. Puree about 2 cups of the soup, return it to the pot and heat through before serving.

This recipe yields 8 servings.

Each serving: 178 calories; 58 mg sodium; 0 cholesterol; 7 grams fat; 1 gram saturated fat; 22 grams carbohydrates; 8 grams protein; 7.88 grams fiber.