In a large soup pot, heat oil over medium heat. Add the onion, carrots and celery and saute until the onion is tender.
Then stir in the bay leaf, oregano and basil. Cook for 2 minutes.
Stir in the lentils, add the chicken broth and tomatoes. Bring to a boil then simmer for 1 1/2 hrs. Then add the spinach and cook until it wilts, stir in the vinegar. Season with salt and pepper and if you like another splash of vinegar, then serve hot.