Preheat the oven to 200 °C.
Heat a heavy-based dry pan and toast the cumin, chillies, ginger and pepper until fragrant.
Remove from the heat and add the salt, sugar and parsley.
Beat the margarine until light and add the spice mixture, beating well together.
Spread the spice paste all over the meat, getting it into the cuts and rubbing it in well.
Put the meat in a large roasting pan and add the stock.
Roast for 30 minutes per 500 g of lamb until tender and juicy.
Pour the pan juices into a small saucepan and reduce.
Serve with the meat.