Heat the oil in a large (preferably non-stick) saucepan (one which you can cover, in a later step), add the lamb and cook for 2-3 minutes on each side or until the lamb has browned; remove and set aside.
Add a little more oil if it is needed (but if you are using a non-stick pan this shouldn't be necessary), then add the onion and garlic and cook for 2 minutes or until they are tender.
Return the lamb to the saucepan with the stock, potatoes and tomatoes and simmer covered for 40 minutes, stirring occasionally.
Add the undrained brown lentils, pumpkin and thyme; season to taste; and simmer uncovered for a further 30-40 minutes or until the lamb is tender.
Serve - garnished with parsley - in large bowls and crusty rolls.