In a large stock pot, heat 2 tablespoons olive oil over medium heat. Add onion, carrots, celery, and potatoes and saute until starting to soften. Add garlic and continue to saute another minute.
Add 6 cups vegetable broth, tomatoes, thyme, basil, oregano, salt and pepper. Bring to a simmer. Stir in lentils and tomato paste. Partially cover pot and simmer for 45 minutes or until lentils are tender.