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.
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.