Marinate the beef in soy sauce, brown sugar, 1 teaspoon sesame oil, and red chili pepper flakes for 10-15 minutes. Set aside.
In the meantime, combine all the sauce ingredients. Stir until everything's all incorporated and the corn starch is completely dissoved.
Heat a wok or wide pan with oil, add the beef, sear until golden brown. Set aside
Use the same pan add more oil if needed. Add garlic, ginger, and onion, saute for a minute or until the onion is tender. Add the carrot and cabbage, stir fry for a minute or until tender.
Add the sauce, cooked beef, noodles, and the remaining marinade. Stir to combine, sprinkle green onions, and drizzle 1 teaspoon sesame oil. Serve warm.