In a bowl, combine the sliced beef with soy sauce, cornstarch, and sesame oil. Allow it to marinate for about 15 minutes.

While the beef is marinating, steam the broccoli florets until they are a vibrant green and tender-crisp, about 3-5 minutes.

In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat. Add the marinated beef in a single layer and cook for about 2-3 minutes until browned and cooked through.

Remove the beef from the pan and set aside.

In the same pan, add the remaining 1 tablespoon of oil; toss in the minced garlic and ginger, sautéing for about 30 seconds.

Return the beef to the pan and add the steamed broccoli.

In a separate small bowl, whisk together the oyster sauce, brown sugar, rice vinegar, and a dash of salt and pepper.

Pour this sauce over the beef and broccoli, gently tossing to combine, and heat through for an additional 2-3 minutes.

Remove the pan from the heat and sprinkle with sesame seeds.

Serve immediately over cooked rice or noodles.