Preheat a large stockpot. When hot, add the olive oil and heat until shimmering.
Add the diced onion and reduce the heat to medium-low. Add the salt and slow cook the onions until they begin to brown. About 12-15 minutes.
Add the garlic, Herbs de Provence and tomato paste. Increase the heat to medium and sauté until the tomato paste becomes a rich, dark red.
Add the carrots, celery and green lentils and stir to coat.
Add the crushed tomatoes, water and bay leaves and bring the soup to a boil.
Reduce the heat and allow the soup to simmer for 1 hour until the lentils have become soft.
Remove the bay leaves and serve the soup with fresh ground pepper and crusty French bread.