To cook a boneless lamb rump mini-roast, preheat your oven to 200°C. Season the lamb generously with salt and pepper, then heat a splash of oil in a heavy-based pan and sear the lamb on all sides until browned. Transfer to a roasting tray and cook in the oven for approximately 25-30 minutes for medium, depending on the size of the roast. Rest for 10-15 minutes, loosely covered with foil, before slicing. Serve with roast potatoes, seasonal vegetables, and rich lamb gravy for a delicious and tender meal.