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.
02 - Cook the noodles according to package instructions until al dente. Drain well, rinse with cold water to stop cooking, and set aside.
03 - Whisk together all sauce ingredients in a small bowl until the brown 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 and set aside.
05 - Add more 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 the beef to the wok. Add cooked noodles and pour in the sauce mixture. Toss everything together for 2-3 minutes until noodles are evenly 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. Serve immediately while hot.