2.Combine juice, sumac, garlic and 1 tablespoon of the oil in medium bowl, add lamb; turn lamb to coat in marinade.
3.Combine eggplant, capsicum, onion, tomato and vinegar with remaining oil in large shallow baking dish. Roast about 25 minutes or until tender. Place vegetables in medium bowl with spinach and parsley; toss gently to combine.
4.Meanwhile, cook lamb on heated oiled grill plate (or grill or grill pan) until cooked as desired. Cover lamb; stand 5 minutes, then slice thinly.
5.Cook cheese on same grill plate until browned both sides. Toast rolls on same grill plate both sides.
6.Spread hummus on four roll halves; top with lamb, vegetable mixture and cheese, then remaining roll halves.
A deep purple-red spice ground from berries grown on a Mediterranean coastal shrub, sumac adds an astringent flavour to both raw and cooked food. It suits poultry, meat and fish as well as it does a salad. Its piquancy was long only associated with Middle Eastern foods, but these days it is used in many different cuisines.