Combine all the ingredients, except for the steak, in a small bowl. Whisk well.
Place the steak in a large bowl and pour the marinade so the steak is completely coated. Marinate in the fridge for at least 10 minutes up to 24 hours.
Preheat the grill to medium heat.
Remove the meat from the marinade and let it sit at room temperature while you heat the grill.
Sprinkle the meat with pepper and place it on the grill. Cook until the internal temperature reaches around 140F, flipping several times.
Leave meat to rest aside for 10 minutes, before slicing it across the grain.
Video
Notes
TO STORE. Let the steak cool to room temperature, place it in an airtight container, and store it in the refrigerator for 3 to 4 days.TO FREEZE. Wrap the leftover flank steak tightly in plastic or foil, then freeze for 2 to 3 months.TO REHEAT. Bring the steak to room temperature, then reheat it in the oven at 250ºF or in a skillet on the stovetop over medium heat.