To prepare the marinade combine the olive oil, lime juice, onions, garlic, saffron, salt and black pepper.
Cut the lamb into 1 cm (1/2") thick and 4-5 cm ( 1 1/2" to 2") long pieces. Do not remove all the fat as you will need it to melt. Marinate overnight (preferably 24 hours) in refrigerator. The container should be covered.
Thread the lamb on long, thin metal skewers. Thread whole tomatoes separately on another skewer. Brush with the marinade. Barbecue for about 5 minutes on each side, turning frequently.
Serve hot with plain rice (Polow or Chelow) or on middle-eastern bread. If served with rice, some sumac may be sprinkled on.