Mix together the oil, garlic, rice vinegar, soy sauce, honey, ginger and green onions in a large shallow container. Add the flank steak and marinate overnight.
When ready to cook, remove the steak from the marinade, brushing off any stuck-on bits. Grill or pan fry the steak.
To pan fry: Heat up a large heavy cast-iron pan over high heat. Add 2 tablespoons (30 ml) of oil and when shimmery, add the steak. Sear for 3 minutes and flip, searing for another 3 minutes. Remove the pan from the heat and let the residual heat cook the steak to your preference 125 degrees for rare and 130 degrees for medium rare. Remove the steak from the pan, set on a cutting board and rest for 10 minutes, covered with foil.
To grill: Preheat one side of your grill to high. Do not heat the other side. Oil the grill and place the steak on the hot side, close the lid and grill until charred, about 3 minutes per side, until the internal temperature is 125 degrees for rare 130 degrees for medium rare. Remove the steak from the grill, set on a cutting board and rest 10 minutes, covered with foil.
cut the steak in thin slices, at an angle, against the grain. Serve with a drizzle of roasted sesame oil and sliced green onions.