Heat large saucepan, add olive oil and onions. when onions are translucent, add carrots.

In about 5 minutes, add celery, garlic and tomatoes.

In 5 minutes, add broth. Bring to a boil, then reduce heat. Simmer for anywhere between 2-6 hours.

Once vegetables are tender, to your liking, add lentils, and simmer for another 10 mins.