01 - In a bowl, combine the sliced flank steak with 1 tbsp soy sauce, cornstarch, and black pepper. Toss well to coat and let sit for 10 minutes to tenderize.
02 - Whisk together 3 tbsp soy sauce, oyster sauce, hoisin sauce, sesame oil, rice vinegar, brown sugar, and water in a small bowl until the sugar dissolves. Set aside.
03 - Prepare lo mein noodles according to package directions. Drain thoroughly and rinse under cold water to stop cooking and prevent sticking. Set aside.
04 - Heat a large wok or skillet over medium-high heat. Add the sesame seeds and toast, stirring constantly, for 2–3 minutes until golden and fragrant. Remove from pan and set aside.
05 - Add 1 tbsp neutral oil to the wok. Add the marinated beef in a single layer and stir-fry for 2–3 minutes until browned on the outside but still pink inside. Remove beef from the pan and set aside.
06 - Add another 1 tbsp oil to the wok if needed. Add minced garlic and ginger, stir-frying for 30 seconds until fragrant. Add broccoli florets and julienned carrot, stir-frying for 3–4 minutes until crisp-tender.
07 - Return the cooked beef to the wok along with the reserved noodles. Pour the prepared sauce over the ingredients. Toss everything vigorously for 2 minutes to coat evenly and heat through.
08 - Stir in the sliced spring onions and remove from heat immediately. Serve the lo mein hot, garnished with the toasted sesame seeds and extra spring onions.