- Toss the sliced flank steak with cornstarch and set aside. 
- In a small bowl, mix soy sauce, hoisin sauce, oyster sauce, and sesame oil. Set aside. 
- Heat vegetable oil in a large skillet or wok over medium-high heat. 
- Add garlic and ginger, sauté for 30 seconds until fragrant. 
- Add beef and stir-fry until browned, about 3–4 minutes. 
- Toss in broccoli and cook for another 2–3 minutes until tender-crisp. 
- Add cooked noodles and sauce mixture to the pan. Toss everything to coat evenly. 
- Sprinkle with green onions and red pepper flakes, if using. Serve immediately.