Pre-heat the oven to gas mark 2, 150°C.
All you do is trim any excess fat from the lamb and cut it into 2.5cm thick rounds. Now tear off a sheet of foil large enough to wrap them in and place in a roasting tin. Arrange the pieces of meat in the centre of the foil.
Next, slice 3 of the garlic cloves into slivers and, using the tip of a sharp knife, make incisions in the lamb and insert the pieces of garlic, distributing them as evenly as possible.
Now grate the zest from the lemons (reserving it for later), squeeze the lemon juice and pour it over the lamb, adding some seasoning. Fold up the foil to make a parcel, place it in the centre of the oven and cook for 3 hours. Just before serving, chop the remaining clove of garlic and the parsley in a mini-chopper and mix it with the lemon zest.
Serve the lamb with the wonderful cooking juices spooned over and sprinkled with the parsley mixture.
Note: this is great served with a Greek salad (cucumber chunks, quartered tomatoes, black olives, red onion slices and crumbled feta tossed with olive oil, lemon and garlic), and Oven-sautéed Potatoes with Red Onion, Garlic and Rosemary.