01 - Combine beef with soy sauce, cornstarch, and sesame oil in a bowl. Mix thoroughly and let marinate for 10 minutes to tenderize.
02 - Prepare noodles according to package directions until al dente. Drain well and set aside.
03 - Whisk together soy sauce, oyster sauce, hoisin sauce, sesame oil, brown sugar, water, and cornstarch until smooth and fully combined.
04 - Heat vegetable oil in a large skillet or wok over medium-high heat. Add marinated beef and stir-fry for 2-3 minutes until browned. Remove beef from pan and set aside.
05 - In the same pan, add broccoli, carrot, and bell pepper. Stir-fry for 2-3 minutes until vegetables are crisp-tender. Add garlic and cook for 30 seconds until fragrant.
06 - Return beef to the pan with cooked noodles and green onions. Pour sauce over everything and toss until evenly coated and heated through, about 2 minutes.
07 - Transfer to serving plates or platter. Sprinkle with toasted sesame seeds and additional green onions. Serve immediately.