In a medium bowl, combine the sliced flank steak with soy sauce, cornstarch, baking soda, and rice wine. Mix well to ensure all pieces are coated. Let marinate for at least 15 minutes (or up to 1 hour in the refrigerator).

In a small bowl, whisk together beef broth, oyster sauce, soy sauce, brown sugar, sesame oil, and cornstarch until smooth and well combined. Set aside.

Bring a pot of water to a boil. Add the broccoli florets and blanch for 1 minute. Immediately drain and rinse with cold water to stop the cooking process. Set aside.

Heat 2 tablespoons of vegetable oil in a wok or large skillet over high heat until just smoking.

Add the marinated steak in a single layer (work in batches if needed to avoid overcrowding). Let cook undisturbed for 1 minute, then stir-fry for another 1-2 minutes until just browned. Remove steak from the wok and set aside.

Add the remaining 1 tablespoon of oil to the wok. Add minced garlic, grated ginger, and the white parts of the green onions. Stir-fry for 30 seconds until fragrant.

Add the sliced bell pepper and stir-fry for 1 minute.

Add the blanched broccoli to the wok and stir-fry for another 2 minutes.

Return the cooked steak to the wok.

Pour the prepared sauce over the stir fry and toss to coat evenly. Cook for 1-2 minutes until the sauce thickens and everything is heated through.

Garnish with sliced green onion tops and sesame seeds. Serve hot with steamed rice or noodles.