Clean the lentils and wash them well in colander. Boil them in plenty of water for 10 minutes and drain. In another pot, heat the oil and sauté the onions. Then add the lentils, the garlic and the carrots, and stir for 2-3 minutes.
Add the finely chopped tomatoes, plenty of water and the bay leaves. Cook the soup until the lentils and other ingredients are soft, approximately 1 hour. Towards the end, add the salt and pepper. Serve the soup in bowls and add vinegar to taste.