In a mortar and pestle or spice grinder, grind black pepper, allspice and cinnamon. In a small bowl, combine pomegranate molasses and spice mixture. Spread glaze over lamb, cover with plastic wrap and marinate in the refrigerator for 30 minutes.

Preheat barbecue grill to medium-high heat.

Season lamb with salt and grill on barbecue for 3 to 4 minutes. Flip meat and grill an additional 3 to 4 minutes, basting with additional leftover glaze. Remove meat from heat and let rest 3 to 5 minutes. Slice lamb against the grain.