1) Heat the olive oil in a large pan and fry the carrot, celery, onion and turnip until softened. 2) Add the garlic and mushrooms and fry for a further five minutes. 3) Add the lentils to the pan. Pour over the stock, add the herbs and tomato puree. 4) Bring to the boil, then reduce the heat and simmer for 45 minutes. 5) Serve with some nice crusty bead.