01 - Toss the sliced flank steak with 1 tablespoon soy sauce, cornstarch, and black pepper in a bowl; let it marinate for 10 minutes.
02 - Whisk together soy sauce, oyster sauce, hoisin sauce, toasted sesame oil, rice vinegar, brown sugar, and water in a small bowl; set aside.
03 - Boil lo mein noodles according to package directions; drain, rinse briefly under cold water, and set aside.
04 - Heat a large wok or skillet over medium-high heat and toast sesame seeds for 2 to 3 minutes, stirring constantly until golden and fragrant; remove and reserve for garnish.
05 - Add 1 tablespoon neutral oil to the wok and stir-fry marinated beef for 2 to 3 minutes until just browned; remove and set aside.
06 - Add another tablespoon of oil if needed, stir-fry garlic and ginger for 30 seconds until fragrant; add broccoli florets and julienned carrot, cooking for 3 to 4 minutes until crisp-tender.
07 - Return beef to the wok along with noodles, pour sauce over, and toss thoroughly to coat and warm through, approximately 2 minutes.
08 - Stir sliced spring onions into the mixture, remove from heat.
09 - Plate immediately and sprinkle with toasted sesame seeds and additional spring onions if desired.