To prepare the stuffing: In a large bowl mix all the ingredients together.
Preheat the oven to 180 C / Gas mark 4.
Place the joint on a chopping board, remove any butcher's string and unroll. Generously season on both sides with salt and pepper. Combine the rosemary, dried herbs and olive oil, then rub the herb mixture all over the joint.
Spread the stuffing mixture evenly over one side of the lamb shoulder, leaving some space at the edges. Re-roll the joint and secure with butcher's string. Place the stuffed lamb shoulder on a metal rack in a large roasting tin.
Roast for 2 hours for medium (25 minutes per 450g plus 25 minutes) or 2 1/2 hours for well done (30 minutes per 450g plus 30 minutes).
Remove from the oven, loosely cover with a sheet of foil and let rest for 15 to 20 minutes before slicing.