01 - Combine sliced beef with soy sauce, cornstarch, and sesame oil in a bowl. Toss thoroughly to coat and let marinate for 10-15 minutes while preparing other ingredients.
02 - Cook noodles according to package directions until al dente. Drain well, rinse thoroughly 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 and set aside.
05 - Add additional oil to the wok if needed. Stir-fry garlic, ginger, white spring onion parts, 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 sauce over everything. Toss vigorously for 2-3 minutes until noodles are evenly coated and beef is heated through.
07 - Remove from heat immediately. Sprinkle with sesame seeds, green spring onion parts, and fresh cilantro. Serve hot while noodles retain their chewy texture.