Add the brown onion, celery, garlic, rosemary, cumin, ground coriander and paprika to the pan. Cook, stirring, for 5 mins or until starting to brown. Add the stock, crushed tomato and 1 cup (250ml) of water. Bring to a simmer. Return lamb to pan. Reduce heat to low. Simmer, covered, for 2 hours or until lamb is very tender. Remove the lamb from the pan. Use two forks to coarsely shred the lamb. Place in a heatproof bowl. Add 1 cup (250ml) of the cooking liquid and toss to combine.