To Finish on the Grill: Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over half of coal grate. Alternatively, set half the burners of a gas grill to high heat. Set cooking grate in place, cover gill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Place the pinwheels on the hot side of the grill and cook without moving until well charred on first side, about 3 minutes. Flip steaks and char second side, about 3 minutes longer. Transfer to cooler side of grill, brush with 1 to 2 tablespoons teriyaki sauce, cover, and cook until an instant read thermometer inserted into the center registers 120°F for medium-rare or 130°F for medium, flipping once half way through cooking and brushing with more sauce. Transfer to a platter, let rest for five minutes, brush with more sauce, sprinkle with scallions, and serve.