Combine all ingredients for the Chimichuri Sauce. Score each side of the steak about 0.125 to 1 cm deep and rub in the sauce, reserving some of the sauce to serve with the meal. Place the meat and marinade in a ceramic or glass pan and marinate overnight in the refrigerator. Remove the meat and extra sauce from the refigerator and allow to sit at room temperature before grilling. Grill the meat over charcoal or under a broiler until medium-rare. Carve the steak immediately accross the grain into strips about 1 cm thick and serve with extra sauce. If the meat is allowed to sit before carving, it will toughen.