Heat your wok on high. While the wok heats up, add oil (1 tbsp) to the marinated beef and give it a quick mix. The oil loosens up the beef slices so they don't clump together, and it helps to seal in the marinade.
After 1-2 minutes, or when the wok is beginning to smoke, add oil (2 tbsp) and swirl it around to coat the wok. Adding the oil when the wok is dry and smoking is the key to preventing sticking and burning.
Let the oil heat up for 30-40 seconds, then add the beef. Spread it evenly around the wok, but let it cook undisturbed for 20 seconds first before beginning to flip the pieces.
Stir-fry the beef until it's about 80% cooked through, or for another 20-30 seconds. Then, take the beef out and set it aside. It'll come back to join the noodles later.
Add more oil (1 tbsp) to the wok, and add the minced garlic. Stir-fry the garlic for 15 seconds.
Add the napa cabbage stems, and cook for 15-20 seconds.
Add the napa cabbage leaves and the green onion whites. Cook for another 20-30 seconds.
Add the carrot strips. Stir-fry everything together, making sure to mix up all the ingredients together. Cook until the vegetables have softened or about a minute.
Add noodles & stir-fry everything
It's finally time to add the noodles! Add them to the wok. Use tongs to separate the noodles so they'll be able to integrate and mingle with the rest of the vegetables. Mix it well for 30 seconds.
Give the stir-fry sauce a quick stir to recombine anything that might have settles, then pour it into the wok. Follow with the pre-cooked beef, and mix everything together. Let the noodles soak up the sauce.
Stir-fry with the beef for 30-40 seconds, then add the sweet peppers, snow peas, and green onion greens. Stir-fry for another 40-50 seconds and give it a taste. We added more light soy sauce (0.50 tbsp), but as always, adjust to your preference.
Add sesame oil (1 tsp) and stir it in for another 1-2 minutes, then turn off the heat.