Using a sharp fork, prick the London broil a few times on each side.
Place it in a ziplock plastic bag.
Pour the marinade over the meat, making sure to coat it evenly.
Squeeze out the excess air, and seal it.
Place it in the fridge to marinate for 4 hours at least, overnight ideally.
When the steak is ready, lightly oil the grill and preheat it to a medium heat.
Remove the beef from the marinade and cook for 15 to 20 minutes per side. It should begin to firm up and still be slightly pink in the very center.
When it is done, shut off the grill and close. Allow the meat to settle for about 5 minutes.
Plate and cut across the grain.