01 - Combine sliced beef, 1 tablespoon soy sauce, cornstarch, and 1 teaspoon sesame oil in a bowl; mix thoroughly and let rest for 10 minutes.
02 - Cook noodles according to package directions, then drain and rinse with cold water; set aside.
03 - Whisk together soy sauce, oyster sauce, chili garlic sauce, rice vinegar, brown sugar, and toasted sesame oil in a small bowl.
04 - Heat 1 tablespoon oil in a large wok or skillet over high heat; stir-fry beef in batches until just browned, approximately 2 minutes; remove and keep warm.
05 - Add additional oil if necessary, then stir-fry garlic and ginger until fragrant, about 30 seconds. Add bell pepper, carrot, and sugar snap peas, cooking 2 to 3 minutes until tender-crisp.
06 - Return beef to wok, add cooked noodles and sauce; toss thoroughly and heat through, about 2 minutes.
07 - Stir in sliced spring onions just before serving.
08 - Serve immediately, topped with sesame seeds, fresh cilantro leaves, and extra spring onions.