Place all the ingredients in a heavy-based flameproof casserole dish with a tight-fitting lid, pouring over the measurement water or stock at the end. Bring to a simmer on the hob.
Cover the casserole dish and transfer to a preheated oven, 150°C (300°F), Gas Mark 2, for about 3 hours until the lamb is meltingly tender.
Remove the casserole dish from the oven and garnish the lamb with sliced spring onions and red chillies. Serve with egg noodles or rice.