1. Mix all the spices together and rub all over the lamb. Leave in a fridge overnight so that the lamb takes on all the flavour of the spices.
2. Preheat oven to 180°C, gas mark 4. Take the lamb out of the fridge and allow to return to room temperature.
3. Put the garlic and onions into a roasting tin with the rosemary, and place the lamb on top. Put into the oven and cook for 2- 2½ hours
4. While the lamb is cooking whisk together the sunflower oil, vinegar and mustard to create a vinaigrette.
5. Separate the leaves of the little gem lettuce, and put in a bowl with the spinach leaves.
6. Bring a pan of salted water to the boil. Top and tail the green beans and drop into the boiling water. After 2 minutes add the peas and mange tout and boil for a further 1 minute.
7. Drain off the vegetables and immediately add to the bowl with the little gem and spinach. Add the watercress and dress all the leaves and vegetables in the vinaigrette.
8. When the meat is cooked through and very soft, take out of the oven and leave to rest. Once rested, sprinkle the fat side of the lamb with the brown sugar and, using a blow torch or under a hot grill, caramelise the sugar and the fat.