Score the lamb
Season lamb and pour over the oil
Combine the spice mix with the yogurt and mix, before pouring over the lamb
Marinate lamb for 1hr, or ideally overnight
Once ready to cook put joint on the bed of onions, and if using a slow cooker, cook on low for 7 hours or on high for 5 hours. If using a casserole dish in the oven, cook for 3.5 hours at 150℃
Once ready the joint should easily shred between two forks
Save the stock and onions for the sauce if you wish