Combine mustard. O.J. vinegar, garlic, salt and pepper. Place flattened lamb in this marinade for 2-3 hours.
Cut sweet potato into finger sized pieces and sauté in olive oil until a little colored. Set aside.
Fry sausages or any other choice of stuffing. Set aside.
Place lamb on a board and lay the sausages and sweet potatoes from one side to the other (short side) as it will make rolling the shoulder easier. Roll the shoulder using the wooden skewers (vertically), to fasten the meat together. Place the chunks of leek and green pepper on the end of the skewers.
Roast at 375 for about 1 hr 30 min, basting often.