Place steak in a large gallon-sized resealable bag. Pour enough Italian dressing in the bag to cover steak. Seal and place in rectangular baking dish. Place in refrigerator and marinate at least 4 hours but it is best if left overnight. Turn occasionally.
When ready to grill the meat, preheat the grill to high.
Sear well on each side, about 1-2 minutes, then cook until desired doneness, a total of about 6 minutes per side for rare and 7 minutes per side for medium-rare (perfect in my opinion).
Remove to cutting board and let rest 5 minutes before cutting.
When carving, cut thin diagonal slices across the grain.
Video
Notes
HOW TO SLICEDetermine how the grain runs in the meat. You will see the fibers fairly clearly in a flank steak running the length of the steak.Place your knife across these fibers and at a 45-degree angle and cut ⅛" to ¼" thick slices. This shortens the fibers in each slice and makes the meat more tender, maximizing tenderness, and making it easier to chew.