In a medium bowl combine the soy sauce, vegetable oil, garlic cloves, brown sugar, tomato paste, paprika, and cayenne pepper. Mix well and set aside.
Rub the salt and pepper all over the London Broil and place in a container.
Pour the marinade over top of the steak. Flip the meat to coat.
Place the meat in the marinade in the refrigerator for at least 2 hours up to 24 hours.
When ready to cook heat a grill to medium high heat. Cook for 5 minutes on one side then flip the meat and cook for 10 minutes on the other side or until the steak registers 135 degrees.
Remove the London Broil from the grill and let it rest for 5 minutes (this allows the temperature to get up to medium).
Slice and enjoy.