In a large pot, heat the olive oil over medium heat. Add the pancetta and cook until crisp, about 6 to 8 minutes.
Add the carrots, celery, and onions and cook, stirring occasionally, until soft and translucent, about 7 to 10 minutes.
Add in the garlic and cook for another 30 seconds.
Add the thyme, oregano, red pepper flakes, pepper, and salt and cook, stirring frequently, for another minute.
Add in the tomato sauce and then the chicken stock. Turn the heat to high and bring the liquid to a boil.
Reduce heat and bring to a steady simmer. Stir in the lentils and bay leaves, partially cover the pot, and let simmer for 40 minutes, stirring occasionally to prevent burning on the bottom. Adjusting the heat, as necessary.
Stir the soup, and if too thick, add more stock. Add the potatoes and cook for another 15 minutes, or until they are tender.
Meanwhile, remove the casings from the sausage links and form small meatballs. Cook them in a medium saucepan over medium heat with a splash of olive oil until cooked and nicely browned
Add the cooked sausage to the soup.
Taste the soup and add salt, if necessary. Remove the bay leaves.
Serve with toasted, crusty Italian bread.
Green lentils work well with this soup, but so do red or brown. Whatever is available at your supermarket will work. You will find dried lentils in the dried beans section of the grocery store.If using dried herbs, use half the amount called for in the recipe.Keep extra stock on hand, in case the soup gets thicker than desired. Simply add the stock until you reach the desired consistency.Omit the pancetta and sausage, and use vegetable stock/broth, in place of the chicken stock, to make this soup vegetarian.The soup will keep in the refrigerator for up to 1 week and freezes beautifully for up to 2 months.