Pour 1 cup of the Italian Dressing over the flank steak. Massage the steak gently in the bag to coat it with the dressing. Put in the refrigerator.
Flip the steak bag over once or twice a day for the next 2 to 3 days. This ensures both sides of the steak are in the marinade
The steak is now ready to grill. Alternately you can put the steak in the freezer, and freeze for up to 6 months. Defrost overnight in the refrigerator when you are ready to use it.
Grill the steak on a preheated BBQ grill. Place the steak on the hot grill and pour some of the marinade over the steak. Continue to add the marinade to the steak as you grill it. Grill to desired doneness. Note if you have a think steak the outer portions will be medium-well done and the center will be medium-rare.
Slice very thin against the grain of the meat and serve.
London Broil can be substituted for the flank steak. It isn't as tender but still delicious. Slicing it very thin after it's grilled helps it to taste more tender.