In a mixing bowl, combine sliced beef with soy sauce, Shaoxing wine, and cornstarch. Let marinate for 10 minutes.
Heat a dry pan over medium heat and toast Szechuan peppercorns until fragrant. Crush them lightly and set aside.
Heat vegetable oil in a wok over high heat. Add dried red chilies, garlic, and ginger, stirring until fragrant.
Add marinated beef and stir-fry until browned, about 2-3 minutes.
Toss in bell pepper and onion, cooking for another 2 minutes to keep them crisp.
Pour in dark soy sauce, hoisin sauce, sugar, and crushed Szechuan peppercorns. Stir well to coat everything.
Taste and adjust seasoning with salt and black pepper. Garnish with scallions before serving.