In a mixing bowl, combine the beef with the marinade ingredients. Cover and set aside to marinate for at least 20 minutes.
In another bowl, mix together the sauce ingredients.
Heat oil in a wok or large skillet over high heat until it begins to smoke. Add the marinated beef slices and spread them out into a single layer. Sear for about 1-2 minutes on each side until browned. Cook in batches if necessary. Remove the beef from the wok and set aside.
In the same wok, add the sliced onion, scallion whites, minced garlic, minced ginger, and dried chili peppers. Stir-fry for a couple of minutes until fragrant and softened.
Pour the prepared sauce into the wok and stir until it thickens slightly.
Add the cooked beef and scallion greens. Stir to coat them evenly with the sauce.
Serve it with rice and enjoy!