Prepare the Spice Rub: Mix sumac, cinnamon, ground cumin, black pepper, and salt.
Apply the Rub: Use olive oil as a binder and apply the spice rub on both sides of the lamb shoulder.
Smoke the Lamb: Smoke at 120°C for the first 4 hours, then increase to 150°C for the last hour to help render the fat.
Check for Doneness: Look for an internal temperature of about 94-95°C and ensure there's little resistance when probing.
Rest the Lamb: Rest for at least half an hour, longer if possible.
Serve: Serve with a simple tahini dressing, flatbreads, and a chunky salad of tomatoes, cucumbers, and red onions.