Trim the flank steak of any excess silver skin and fat. Place in a 9 by 13 inch baking pan and sprinkle on all sides with the kosher salt.
In a small bowl mix together the olive oil, minced garlic, black pepper and red chili flakes. Pour over the flank steak and turn to coat all sides of the steak with the seasoned oil. Marinate in the refrigerator for at least 1 hour, up to 24 hours.
Preheat grill with a medium high flame for at least 15 minutes and brush thoroughly to clean.
Place ¼ cup vegetable oil in a small dish. Fold a paper towel into a small square and hold with a pair of tongs. Just before adding the steak dip the paper towel into the vegetable oil and rub on the grill grates to coat with oil.
Turn the steak once again to redistribute the seasoned oil on all surfaces of the steak. Place on the oiled grill and cook for about 3-4 minutes, then using a pair of tongs turn the steak 90 degrees to create grill hash marks. Cook for an additional 5 minutes.
Turn the steak and cook for 6-8 minutes, or to the desired doneness.
Remove the steak to a large plate, tent with foil and let it rest for 5-10 minutes. Place on a cutting board and slice across the grain into ½ inch thick slices and serve.