In a mixing bowl, combine thinly sliced flank steak with baking soda, low-sodium soy sauce, sesame oil, white pepper, and cornstarch. Let it marinate for at least 20 minutes.

In a separate bowl, whisk together oyster sauce, Sichuan peppercorns, black pepper, Shaoxing wine, soy sauces, sugar, and additional cornstarch. Set it aside.

Place a wok over high heat, add ⅓ cup of vegetable oil, and heat until it shimmers.

Carefully add half of the marinated beef to the hot wok and sear for 2-3 minutes until browned. Repeat with remaining beef.

Drain excess oil from the wok, leaving about 2 tablespoons. Sauté minced garlic for about 30 seconds until fragrant.

Add sliced onions and red bell pepper to the wok. Stir-fry for approximately 1 minute until tender.

Return the seared beef to the wok, pour in the prepared sauce, and toss everything together quickly until well-coated.

Drizzle with sesame oil and serve over rice or noodles.