In a food processor add the onion and garlic until finely diced. Add the rosemary, thyme and sage leaves, then process again. Add bread and process until a seasoned breadcrumb mix is created.
Tip the breadcrumbs into a bowl then add the egg, salt and pepper. Combine with hands or a spoon until egg is absorbed.
Lay out the boneless, butterflied leg of lamb over strings laid about 3cm apart. Add the stuffing over the lamb to create an even roll. Roll the lamb with the stuffing in it then tie the strings to secure for cooking. (Yes, this can be a juggling act.)
Roast or cook in a hooded BBQ at 180 degrees C for one hour, then check regularly until it is cooked to your preferred doneness.