Whisk together soy sauce, balsamic vinegar, powdered ginger, Worcestershire sauce, olive oil, fresh lemon juice, garlic powder, brown sugar, and red pepper flakes to create the London Broil marinade.
Pour the marinade into a zip-lock bag, then add London Broil steak. Shake well and refrigerate to marinate for at least 4 hours up to overnight.
Remove the steak from the bag and set aside. Keep the marinade! You will use it later to make a sauce. Season steak with salt and pepper to taste on both sides.
Add to the grill at 400°F for 5 to 8 minutes on each side. Use a meat thermometer for best results.
Meanwhile, pour steak marinade from the bag into a skillet over medium heat on the stove. Mix and let it simmer and thicken until it forms a sauce.
Remove your steak from the grill and let it rest 10-15 minutes. After resting, slice thinly and serve with sauce on top.