Cut flank steak against the grain into thin strips against the grain. Cut it as thin as you can and place the strips in a small mixing bowl.
In the small mixing bowl, combine soy sauce, brown sugar, sesame seeds, sesame oil, garlic, crushed red pepper flakes, ginger, and oyster sauce.
Mix the meat strips with the spices until well coated. Let marinate for 1 hour in the refrigerator.
After marinating, heat a large heavy skillet or wok over high heat. Add in the meat and cook on high until meat is cooked through. This should take less than 5 minutes.
Serve hot by itself or over rice and top with green onions.
Meat Options: Instead of flank steak, you can also use skirt steak, ribeye, sirloin, or brisket. Even ground beef can be used for an inexpensive version.For ground beef, instead of marinating, simply make the marinade and keep it separate. Once your ground beef is cooked through, drain it well, then add in the marinade as a sauce to flavor the ground beef. Asian Pear: this is a traditional ingredient in Bulgogi. If you don't have one, have an allergy, or they are out of season, you can simply omit it.