1. To butterfly and stuff a flank steak, make a lengthwise cut horizontally through steak, cutting to within 1/2 inch of opposite side. Spread open; cover with plastic wrap.
2. Working from the center to the edges, pound with flat side of meat mallet to even thickness (about a 12-inch square).
3. Remove plastic wrap. Sprinkle pepper over entire cut surface; set aside.
4. For filling, combine bread crumbs, Romano cheese, parsley, pancetta or bacon, and garlic. Sprinkle filling over the cut surface of the steak.
5. Roll up so that grain runs lengthwise. Tie in several places with heavy kitchen string. If necessary, cut roll in half to fit pan.
Be careful not to cut completely through the meat or you may wind up with two or three pieces of meat rather than one large, thin one.