FIRST: Preheat the oven to 180 degrees C, 350 degrees F., Gas Mark 4.
SECOND: Put the garlic, ginger, lemon rind, parsley, mint and rosemary in a food processor and blast for a minute or so until everything is finely chopped. Switch on again and add the olive oil slowly until you have a lovely bright green mixture. Set aside.
THIRD: Place the lamb joint in a roasting tin with the onion and water. Roast in the oven, allowing 20 to 25 minutes per pound (half kilogram).
FOURTH: Thirty minutes before the end of the roasting time, remove the joint from the oven. Spread the herb mixture all over it. Return to the oven and finish roasting.
FIFTH: Keep an eye on the water level and top up if necessary. When the lamb is cooked remove from the oven and keep warm. Throw away the onion and remove excess fat.
SIXTH: Add a good dash of wine to the pan juices. Boil up and reduce to a nice syrup.
FINALLY: Season the jus and serve with the sliced lamb.