Prepare the Marinade. Stir together all the ingredients until well-blended.
Score the top of the steak, about 1-inch cuts apart, so the marinade can seep in. Place in in a resealable bag and pour the marinade over it. Seal and refrigerate for up to 12 hours (or no less than 2 hours).
Remove the steak from the marinade and blot completely dry. Place on a plate, cover with plastic wrap, and let come to room temperature. Boil down the marinade to make a sauce.
Heat the grill pan until very hot and brush with oil.
Season the steak generously with salt and pepper and place on the grill pan. Sear for 2 minutes per side until grill marks appear. Once the steak is on the grill, do not move it until it's time to turn it, so that it forms a nice crust. If you want crisscross grill marks, move the steak once halfway in between the cooking time on each side.
Place the seared steak on the baking sheet and continue to cook in a preheated 200°C (390°F) oven for another 10 minutes using the convectional heat function.
Remove the steak from the oven and let it rest for 10 minutes before carving or slicing.
Slice the steak against the grain on the bias (diagonal). Top with with chopped scallions and drizzle with reduced marinade sauce before serving.