while it might violate the rules of lots of experts - slice it on the bias - and thin - real thin - & do it pretty swiftly so it is fresh off the grill - have never had an issue with 'too tough' - and never have leftovers!
^^^ This! A thin bias cut gets you wonderful, flavorful meat that is not chewy. For those interested, below is my recipe.
1 2-to-2 1/2 pound London broil
For marinade
4 large garlic cloves, minced
4 tablespoons balsamic vinegar
4 tablespoons fresh lemon juice
3 tablespoons Dijon mustard
1 1/2 tablespoons Worcestershire sauce
1 tablespoon soy sauce
1 teaspoon dried oregano, crumbled
1 teaspoon dried basil, crumbled
1 teaspoon dried thyme, crumbled
2/3 cup olive oil
For spice, include
1/2 teaspoon dried hot red pepper flakes
1/8 teaspoon hot paprika
Preparation
Make the marinade by whisking together all the ingredients until combined well.
To tenderize the meat, I use a regular long-pronged fork. Quickly and firmly poke the London broil all over both sides of the meat, making sure to “open” each side of the meat.
Put London broil in a large resealable plastic bag and pour marinade inside. Seal bag, pressing out as much excess air as possible. Set in a shallow dish and place in the refrigerator for at least 12 hours. (The dish is just incase there is any seepage of liquid.)
When ready to grill, prepare a charcoal brazier with quality charcoal. Make certain the coals are white, hot and spread evenly within the brazier. Take the London broil out of the bag and place on a lightly oiled grill rack about 4 inches from the glowing coals. Turn the meat every three minutes for a total of 15 minutes (five times). Internal temp. should register 135°F. to 140°F., on a meat thermometer for rare-medium meat. Biggest mistake is to try and cook the meat beyond 140°F as it dries out the meat and wrecks the flavor. Transfer meat to a cutting board and let stand for five minutes minutes. Using a saber knife, cut meat diagonally across the grain into thin slices.
I also serve with garlic butter to drizzle over the meat. Sometimes I'll offer steak rolls to put the meat on with the garlic butter.