To make Tabouli, cover burghul with boiling water and stand for 10 minutes. Drain and rinse with cold water. Drain again. Wrap burghul in a clean tea towel and wring out to dry. Place burghul in a bowl with remaining Tabouli ingredients. Season to taste and toss to combine.
Preheat barbecue on high. Sprinkle lamb with sumac and cook for 2-3 minutes each side. Stand lamb for 5 minutes then thinly slice on diagonal.
Arrange lamb and lebanese bread on a platter. Place hummus and Tabouli in bowls and let everyone serve themselves.