OPTIONAL: Marinate steak for at least two hours in the refrigerator. Then, season steak with salt on both sides. Leave on a clean plate at room temperature for 45 minutes. When ready to cook, brush olive oil on the grill grates. Preheat the grill to high heat, or 450-500 degrees for a gas grill
Sprinkle salt and pepper on each side of the flank steak, if desired. Transfer steaks to the grill, and sear for 3-4 minutes on each side, flipping only once
Check the steak's temperature on the thickest part. If it needs some more time to reach your desired doneness, move it to a low-heat side of the grill for just another minute or two
Move steaks to a clean plate or cutting board. Tent with aluminum foil and rest for five minutes. Slice against the grain, if desired, to serve