01 - Combine beef slices with soy sauce, oyster sauce, cornstarch, and sesame oil in a bowl. Marinate for 15 minutes.
02 - Cook egg noodles according to package instructions. Drain thoroughly and allow to cool slightly.
03 - Heat 2 tablespoons vegetable oil in a large nonstick or cast-iron skillet over medium-high heat. Add cooked noodles, pressing into an even layer. Fry undisturbed for 4 to 5 minutes until golden and crispy on the bottom. Flip in sections if needed and crisp the other side for 3 to 4 minutes. Remove and place on a serving platter.
04 - Add one tablespoon vegetable oil to the same pan. Stir-fry marinated beef for 2 to 3 minutes until just cooked through. Remove and set aside.
05 - Add garlic, bell pepper, carrot, and snap peas to the pan. Stir-fry for 2 to 3 minutes until just tender.
06 - Mix all sauce ingredients in a bowl. Pour into the pan, simmering and stirring until thickened slightly, about 2 minutes.
07 - Return beef and any accumulated juices to the pan. Add spring onions and toss to coat evenly with the sauce.
08 - Spoon the beef and vegetable mixture over the crispy noodles. Serve immediately.