01 - Combine the sliced beef with soy sauce, cornstarch, and sesame oil in a bowl. Toss to coat thoroughly and let marinate for 10–15 minutes while preparing other ingredients.
02 - Cook noodles according to package instructions until al dente. Drain well, rinse under cold water to stop cooking and prevent sticking, then set aside.
03 - Whisk together soy sauce, oyster sauce, hoisin sauce, brown sugar, rice vinegar, and red pepper flakes in a small bowl until sugar completely dissolves.
04 - Heat 1 tbsp oil in a large wok or skillet over high heat. Add marinated beef in a single layer and sear for 1–2 minutes per side until browned but still tender. Remove beef from wok and set aside.
05 - Add additional oil to the wok if needed. Stir-fry garlic, ginger, white parts of spring onions, bell pepper, carrot, and sugar snap peas for 2–3 minutes until just tender-crisp.
06 - Return beef to the wok. Add cooked noodles and pour in the sauce mixture. Toss everything together for 2–3 minutes until noodles are thoroughly coated and beef is heated through.
07 - Remove from heat. Sprinkle with sesame seeds and green parts of spring onions. Top with fresh coriander or cilantro leaves and serve immediately.