1. Preheat the oven to 180ºC/350ºF/gas mark 4. Cut small slits in the lamb and insert the slices of root ginger. Place the joint in a ovenproof roasting dish and cook, uncovered, in the centre of the oven for 30 minutes.
2. Remove the lamb from the oven, place the vegetables in the roasting dish, season and return to the centre of the oven for a further 35 minutes.
3. Meanwhile, to make the glaze, place the grated fresh root ginger, soft brown sugar and the lime juice in a saucepan and bring to the boil. Simmer for 1-2 minutes until thickened and sticky.
4. Remove the lamb and vegetables from the oven and spread the glaze on to the joint. Once the lamb is coated, give the vegetables a good stir to ensure they have a good covering of the lamb juices. Return to the centre of the oven for 30 minutes.
5. Serve the roast lamb with the roasted vegetables and steamed mangetout and broccoli florets.