Grilled Stuffed Flank Steak With Ginger & Teriyaki Glaze

¼ cup rice bran oil, plus 2 tsp if finishing indoors
2 cups thin sliced spring onions, plus more for garnish
3 tbsp grated fresh ginger
1 whole flank steak, 1 kg, trimmed of excess fat
1 tsp SIDS SALT & PEPPER
Basic Teriyaki Sauce

Heat oil in a small saucepan over medium-high heat until shimmering. (a single spring onion dropped into it should sizzle immediately) Meanwhile, combine spring onions and ginger in a medium bowl then season well with SIDS SALT & PEPPER. When oil is hot, pour over spring onions and ginger. It should sizzle for a few seconds. Let cool.
Lay steak on a cutting board with grain running parallel to the edge of the counter. Trim left and right edges to form a clean rectangle and reserve scraps for another use. Hold steak flat with your non-knife hand and, with a sharp boning knife, carefully butterfly the steak, leaving the back edge attached by 1 cm of meat. Open up steak and flatten the seam gently with your hand to form a large perfect rectangle.
Season steak on exposed side with SIDS SALT & PEPPER. Spread spring onion-ginger mixture over steak, leaving a 2 cm border at the top and the bottom.
Carefully roll the steak away from you (the grain should run width-wise), tightening as you go until it is rolled into a cylinder. Let it rest with its seam-side down.
Tie the beef tightly with twine, spacing the ties evenly every 3 cm. Insert a skewer through each piece of twine. Using a sharp knife, carefully cut between the ties to make the pinwheels. Season with SIDS SALT & PEPPER.
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 grill 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 1-2 tablespoons teriyaki sauce, cover, and cook until an instant read thermometer inserted into the center registers 48°C for medium-rare or 54°C 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 spring onions, and serve.
To Finish Indoors: Adjust oven rack to centre position and preheat oven to 200°C. Heat 2 teaspoons oil in a large skillet over high heat until almost smoking. Add steaks and cook, turning every 20 seconds, until well browned on both sides, about 4 minutes total. Transfer to a wire rack set in a foil-lined rimmed baking sheet. Brush with teriyaki sauce and transfer to oven. Cook until an instant read thermometer inserted into the center registers 48°C for medium-rare or 54°C for medium, flipping once half way through cooking and brushing with more sauce, about 2-5 minutes total. Transfer to a platter, let rest for five minutes, brush with more teriyaki sauce, sprinkle with spring onions, and serve.