Combine the marinade ingredients in a glass bowl and whisk together to combine thoroughly.

Place the London broil steak in a large, re-sealable bag.

Pour in the marinade and seal the bag, squeezing out as much air as possible and then place the bag in a refrigerator for 4 - 6 hours or overnight.  Turn the bag at least once during that time to make sure all of the sides of the steak get some soy lovin'.

Light your grill to high heat.  We are going to cook this now-somewhat-leaner tough hunk of meat quickly over high, direct heat until around medium-rare.  Remember, the longer you cook an already tough cut of meat, the tougher it will be.  I recommend to err on the side of rare because you can always stick it back on for a few minutes if you really feel the need.  Once it is over-cooked though, you might as well call up the pizza guy while the kids fling around your new leather frisbee in the backyard.

Remove the marinated London broil from the bag and place on the hottest part of the grill.

Grill with the lid open 5 - 7 minutes per side (we always rotate half way through to get those nice looking grill marks, right?).

Once it has grilled for a total of 10 - 14 minutes, remove the grilled London broil from the grill and place on a cutting board and allow to rest for about 5 minutes.

Now here is the other key to getting the maximum tenderness out of this cut of meat.  Using a sharp knife, slice the meat thin against the grain.  For more detailed directions on how to do that, check out these instructions, but here are the Cliff notes.  The grain on the London broil should be obvious once you pick it up on one side with some tongs and bend the meat.  Find the direction of the grain (9 times out of 10, the grain runs the long length of the cut) and then start slicing thin, perpendicular to the grain like so: