This makes a thick soup that smells amazing and tastes just as good. If you reheat it for lunch at work, everyone will ask what you have that smells so good. It also freezes well for leftovers.
Cook the potatoes a little over half way before chopping. (I microwave them on high for about 5 minutes.).
In a large soup pot, heat oil over medium heat. Add onions, carrots and celery. Saute until onion is tender. Stir in potatoes, garlic, oregano, basil, and pepper. Cook for 1-2 more minutes.
Stir in water, broth, tomatoes, tomato juice, and bay leaves. (The liquid added should total 8 cups.) Bring to a boil. Add lentils and return to a boil. Reduce heat and simmer uncovered for at least 1 hour.
Cook frozen spinach separately, by the package directions, or skip this step if using fresh spinach. Add the spinach and vinegar to the soup in the last 5 minutes of simmering.