In a small bowl, whisk together the soy sauce, honey, cornstarch and red pepper flakes. Set aside.
Heat the oil in a large skillet over medium-high heat. Add the sliced beef. Stir-fry the beef until browned, about 3-4 minutes.
Add the garlic and ginger and cook, stirring, 1 more minute.
Add the soy sauce mixture. Reduce the heat to medium and stir-fry until the beef is well coated and the sauce has thickened, about 2 minutes.
Turn the heat off. Spoon the Korean beef and the pan juices into plates or bowls. Top with the green onions and sesame seeds, drizzle with the sesame oil, and serve.
Video
Notes
*You can try replacing the honey with a sugar-free liquid sweetener. I haven't tried it myself, though.