If you have time, soak the lentils overnight in a bowl with lots of water. If not, put the lentils in a large pot and cover them with water. Boil for 2-3 minutes, rinse and drain. Clean the pot, put 5 cups of water (or vegetable stock) over medium heat.
Add the lentils, the onions, garlic, carrots, celery, and bay leaves. Cover the pot and simmer over medium to low heat for 30 minutes. Soaking and sprouting reduce considerably the cooking time. If the lentils are soft enough, proceed immediately to the next step.
Add the passata or chopped tomato and/or the dissolved tomato paste*. Add the turmeric and cumin and season to taste. Simmer for another 15 minutes until the lentils are soft.
Adjust the amount of water/vegetable stock whether you like watery soup or thick soup. If you add more liquid, it should be hot. Add the olive oil 2-3 minutes before you remove the pot from the heat.
Serve each plate with 1 tablespoon of red wine vinegar.