Heat oil over medium heat in a large pot or dutch oven.
Once oil is hot, add onions, celery, carrots, and a dash of salt. Sauté for about 7 minutes.
Add garlic and sauté for another 2 minutes. Stir in the salt, Italian seasoning, and bay leaves. Sauté for another minute. Add green beans, vegetable broth, water, tomato paste, diced tomatoes, potato, and lentils. Give it a stir, bring to a boil, then simmer (covered) on low for 35-45 minutes, or until lentils are tender.
Stir in spinach and balsamic vinegar. Season with salt and pepper to taste.