In a medium bowl, combine the beaten egg, sliced flank steak, grated ginger, vegetable oil, and salt. Toss everything together until the beef is well coated. Cover and let it marinate for 15–20 minutes.

While the beef is marinating, mix the broth, Shaoxing wine, soy sauce, Chinkiang vinegar, sugar, cumin powder, and cornstarch in a separate bowl. Whisk until well combined.

Heat a large skillet or wok over medium-high heat, add a tablespoon of vegetable oil, then add the marinated beef in a single layer. Cook for 2–3 minutes until golden brown, flip and brown for another 1–2 minutes. Transfer to a plate.

In the same skillet, add more oil if needed, then sauté chopped green onions, garlic, and grated ginger over medium heat until fragrant, about 30 seconds. Add sliced bell peppers and baby bok choy, stirring for about 1 minute.

Pour the prepared sauce into the pan with the sautéed vegetables, stirring constantly until it thickens, about 1–2 minutes. Return the cooked beef to the skillet, tossing everything together to coat well. Serve over steamed rice.