Add all ingredients in a shallow dish, and stir to combine. Add flank steak. Alternatively, put the in a big ZipLock bag, seal it completely and then let the kids shake it to mix the ingredients.
Let the flanks steak marinade for 8 hours or overnight.
Preheat grill on high.
Cook on one side for 5-6 minutes, and then flip and cook for another 4-5.
Allow meat to rest for 15 minutes.
Cut and serve. Note: It is important to cut the flank steak against the grain. The result will be a more tender cut. Cutting in this way ensures you are breaking up the muscle fibers, and the meat won’t be as tough to chew.