Chop all the vegetables for the soup.
Set a large 6-8 quart soup pot over medium heat. Add the oil to the pot. Once hot, add the chopped onions, carrots, celery, and garlic. And sauté for 3-5 minutes until the onions are soft.
Add the vegetable broth, canned tomatoes, dried lentils, tomato paste, and Italian seasoning. Stir well to make sure the lentils don't stick together.
Bring to a boil, then lower the heat if needed and simmer the soup for 20 to 25 minutes, stirring occasionally. You can partially cover the pot while cooking for less splatter.
The soup is ready when the lentils are soft and the base has thickened. Taste, then salt and pepper as needed.
