Slice the steak thinly against the grain into bite-sized strips, about 1/4 inch thick. In a large mixing bowl, combine the sliced steak with 2 tablespoons soy sauce, 1 teaspoon cornstarch, 1 teaspoon sesame oil, and 1/4 teaspoon black pepper. Toss to coat evenly. Let marinate at room temperature for at least 10-15 minutes while you prepare other ingredients.

In a small bowl, whisk together 1/4 cup soy sauce, oyster sauce (if using), brown sugar, rice vinegar, 1/4 cup water (or broth), and 1 tablespoon cornstarch until smooth. Set aside.

Ensure your broccoli florets are bite-sized. Mince the garlic and grate the fresh ginger.

Heat 1 tablespoon of vegetable oil in a large wok or skillet over high heat until shimmering. Add half of the marinated steak in a single layer, ensuring not to overcrowd the pan. Cook for 1-2 minutes per side until nicely browned, then remove to a clean plate. Repeat with the remaining steak, adding a little more oil if needed. Set all cooked steak aside.

Add the remaining 1 tablespoon of vegetable oil to the hot wok. Add the broccoli florets and stir-fry for 3-5 minutes, until bright green and tender-crisp. If they start to dry out, add 1-2 tablespoons of water and cover for 1 minute to steam slightly.

Add the minced garlic and grated ginger to the wok with the broccoli. Stir-fry for another 30 seconds until fragrant.

Return the cooked steak to the wok with the broccoli and aromatics. Give the prepared stir fry sauce a quick re-whisk, then pour it over everything in the wok.

Stir continuously for 1-2 minutes until the sauce thickens and coats all the steak and broccoli. Remove from heat immediately.

Garnish with toasted sesame seeds and sliced green onions, if desired. Serve hot, ideally with steamed rice or noodles.