In a bowl, whisk together all but the last 3 ingredients.
Place the flank steak in large deep dish.
Pour in the marinade over the flank steak to cover the meat.
Cover the dish with shrink wrap and refrigerate for a day (see note below).
Preheat the BBQ to 450 ºF
Remove the meat from the marinate and discard the marinade.
Let the meat sit for about 20 minutes to raise the temperature.
Sprinkle the remaining salt and black pepper over the flank steak.
Place the meat on the hot grill and cook for about 3 to 4 minutes with the lid closed.
Open the lid and rotate the meat about 45 degrees and close the lid for another 3 minutes. This will create those beautiful crosshatch grill marks.
Flip the meat over and repeat the last two steps.
Adjust cooking times to suit your doneness preferences. We aimed for around 140 ºF, somewhere between medium rare and medium. Use a meat thermometer to test the temperature.
Place the cooked meat on a serving dish and cover/tent with aluminum foil to let the meat rest for about 10 to 15 minutes.
Slice the meat and serve hot with your favourite side dishes. Enjoy!
You can marinate the meat for as little as 4 hours or as much as a day.