Soak the lentils in water for a few hours. Fry the onion in oil until lightly coloured. Add the tomatoes and sauté for a minute. Add the drained lentils, cover with water and simmer gently for about ½ hour until they are tender, adding water as required, then season with salt and pepper, add parsley and vinegar and cook until the lentils are done the liquid absorbed.
Taste and adjust th