1.Heat half the oil in a large frying pan; cook potatoes until browned. Transfer to a 4.5-litre slow cooker.
2.Make small cuts in lamb at 2.5cm intervals. Press rosemary into cuts. Combine parsley, oregano, garlic, rind, juice and remaining oil in a small bowl; rub mixture all over lamb and season.
3.Cook lamb in same heated pan until browned all over. Place lamb in cooker on top of potatoes; add stock. Cook, covered, on low, 8 hours.
4.Remove lamb and potatoes. Cover lamb and stand 10 minutes before slicing.
5.Serve lamb with potatoes and sauce.