Use a 6-quart slow cooker. (If your lamb has a netting on it, cut it away using scissors.) Place the meat into the slow cooker insert.
In a small mixing bowl, stir together the apricot preserves, mustard, garlic, rosemary, salt, and pepper.
Smear this paste evenly over all sides of the meat. Do not add water. Cover and cook on low for 8 hours, or until the meat has relaxed, begun to lose shape, and can easily be pulled apart with two large forks. Remove the meat and let it sit for 10 minutes before slicing with a sharp knife.