Heat half the oil in a stock pot over medium-high heat. Add the lamb and cook, turning, for 4-5 minutes or until browned. Transfer to a plate.
Heat the remaining oil in the pot. Add the pancetta, carrot, celery and onion. Stir for 8 minutes or until soft. Add the garlic and rosemary and stir for 1 minute. Add the lamb.
Add the stock, tomato, barley and bay leaves to the stockpot. Cover and bring to the boil. Reduce heat to low and simmer for 2 hours or until lamb is tender and falls apart when tested. Transfer the lamb to a plate. Discard bones and coarsely shred meat. Skim and discard any excess fat from soup. Add the shredded lamb and season.
To make the gremolata, combine the parsley, lemon rind and garlic in a small bowl.
Divide the soup among serving bowls and sprinkle with gremolata.