In a bowl, combine the sliced flank steak with soy sauce, cornstarch, and vegetable oil. Let it sit for at least 15 minutes.

In a large skillet or wok, heat 1 tablespoon of vegetable oil over medium-high heat until hot and shimmering.

Add the broccoli florets and stir-fry for 2–3 minutes until bright green and slightly tender. Remove the broccoli from the pan and set aside.

Add the remaining tablespoon of vegetable oil to the skillet. Once heated, lay the marinated beef in a single layer and cook for 2–3 minutes until browned and cooked through. Remove the beef and set aside.

Add the white parts of the scallions, minced garlic, and ginger to the skillet. Sauté for about 30 seconds until fragrant.

Return the broccoli and beef to the skillet. Pour in the beef broth, soy sauce, oyster sauce (if using), and sesame oil. Stir gently to combine and cook for an additional 1–2 minutes until heated through.

Season with salt and pepper to taste, adjusting as needed. Garnish with the green parts of the scallions just before serving.

Serve hot over steamed rice or noodles.