01 - Combine sliced flank steak with 1 tbsp soy sauce, cornstarch, and sesame oil in a medium bowl. Mix thoroughly to coat and let marinate for 10 minutes at room temperature.
02 - Whisk together 2 tbsp soy sauce, dark soy sauce, vinegar, Szechuan chili bean paste, hoisin sauce, sugar, and water in a small bowl until sugar dissolves completely.
03 - Heat 1 tbsp vegetable oil in a large wok or skillet over medium-high heat until shimmering. Add green beans and stir-fry for 4-5 minutes until skins blister and beans are just tender. Transfer to a plate and set aside.
04 - Add remaining 1 tbsp oil to the wok. Add crushed Szechuan peppercorns and fry for 30 seconds until fragrant, being careful not to burn them.
05 - Add marinated beef to the wok in a single layer. Stir-fry for 2-3 minutes until browned on edges and just cooked through. Push beef to the sides of the wok, clearing the center.
06 - Add garlic, ginger, scallions, and sliced chili to the center of the wok. Stir-fry for 1 minute until fragrant, then combine with the beef.
07 - Return green beans to the wok. Pour in prepared sauce and toss everything together. Cook for 2-3 minutes until sauce thickens slightly and coats all ingredients evenly.
08 - Transfer to a serving platter and serve immediately while hot. Accompany with steamed jasmine or brown rice if desired.