In a mixing bowl, whisk together the soy sauce, oyster sauce, and cornstarch until smooth. Add the thinly sliced beef steak to the bowl, ensuring each piece is well-coated. Cover and let it marinate for at least 15 minutes at room temperature.

Heat the vegetable oil in a large skillet over medium-high heat. Once shimmering, add the minced garlic and fresh ginger, stir-frying for about 30 seconds until they become fragrant and golden.

Add the marinated beef to the skillet, spreading it out in a single layer. Allow it to sear undisturbed for 1-2 minutes, until slightly browned. Then, stir-fry the beef for another 2-3 minutes until it's mostly cooked.

In the same skillet, toss in the sliced green and red bell peppers along with the onion. Stir-fry for 2-3 minutes, or until the vegetables are tender-crisp.

Return the cooked beef to the skillet with the vegetables. Add the black pepper and sesame oil, stirring well to combine all of the ingredients. Let everything cook together for an additional 2 minutes.

Once cooked, sprinkle the sliced green onions and toasted sesame seeds generously over the Sizzling Chinese Pepper Steak.

Serve your flavorful Sizzling Chinese Pepper Steak hot over a bed of steamed white or brown rice.