Preheat the oven to 200°C, gas mark 6. Place the lime pickle, sugar, vinegar and coriander in a small food processor and pulse until fine.
Place the lamb in a large deep-sided roasting pan and rub with the marinade.
Add the garlic, water and ginger to the pan and sprinkle with the salt and pepper. Cover with aluminium foil and cook for 2½ hours or until tender.
Remove the foil, spoon over the cooking liquid and cook, uncovered, for a further 30 minutes or until dark golden brown. Serve immediately.