Preheat the oven to 130°C fan-forced. Score the fat-side of the lamb. Combine 1 tablespoon of the oil with paprika, cumin, coriander and salt and pepper then rub all over the lamb.
Heat a deep, flameproof roasting pan or baking dish over a medium-high heat. Add the remaining oil, then the lamb, skin-side down. Cook until the lamb is well browned all over. Remove the lamb to a tray. Turn the heat down to medium, add the anchovy fillets and stir until dissolved. Add the onions and garlic and cook for 5 minutes until soft, then stir in the mushrooms and cook for 3 minutes. Pour in the stock and bring to the boil. Turn the heat off.
Place the lamb on top of the mushrooms. Add the lemon wedges. Place a sheet of baking paper right down on the surface of the lamb, then cover tightly with a lid or 2-3 layers of foil. Roast for 5-6 hours or until lamb meat falls from the bone easily.
Strain the juices into a jug. Carefully skim the excess fat from the surface of the juices then pour 1-1½ cups juices back over the lamb.
Preheat grill on high heat. Place the lamb under the grill to crisp up the skin if desired. Combine the parsley, lemon rind and almonds and scatter over the lamb. Serve with warm flat-bread and yoghurt.