Preheat oven to 200ºC (400ºF/Gas 6).
Place a rack in a roasting pan and add 1 cup water to the pan. Use a small sharp knife to cut slits all over the surface of the lamb. Poke the garlic slices and sprigs of oregano into the slits. Place the lamb on the rack in the roasting pan and roast for 30 minutes.
Combine the honey, mustard and lemon juice. Brush over the lamb and return to the oven for a further 20 minutes for medium or 30 minutes for well-done. Remove lamb from oven, cover loosely with foil and set aside in a warm place for 15 minutes to rest.
Carve the lamb and serve accompanied with vegetables & beans.