01 - Combine the beef with soy sauce, cornstarch, and sesame oil in a bowl. Mix thoroughly and let marinate for 10 minutes to tenderize and infuse flavor.
02 - Cook the noodles according to package directions until al dente. Drain well and set aside, tossing with a small amount of oil to prevent sticking if needed.
03 - Whisk together soy sauce, oyster sauce, hoisin sauce, sesame oil, brown sugar, water, and cornstarch in a small bowl until completely smooth and the cornstarch is dissolved.
04 - Heat vegetable oil in a large skillet or wok over medium-high heat. Add the marinated beef slices and stir-fry for 2-3 minutes until browned on the edges. Remove beef from pan and set aside.
05 - Add broccoli, carrot, and bell pepper to the same pan. Stir-fry for 2-3 minutes until vegetables are crisp-tender. Add garlic and cook for 30 seconds until fragrant.
06 - Return the beef to the pan along with cooked noodles and green onions. Pour the sauce over the mixture and toss everything together for about 2 minutes until evenly coated and heated through.
07 - Transfer to a serving platter or individual plates. Sprinkle with toasted sesame seeds and additional sliced green onions for garnish.