1 lb sirloin tips or flat iron steak, trimmed
4 Tbsp low-sodium soy sauce, divided
1 tsp Sichuan peppercorns, ground
6 Tbsp grape seed or other neutral oil
3 Tbsp chili-garlic sauce
5 medium garlic cloves, finely grated
4 tsp unseasoned rice vinegar
2 tsp toasted sesame oil
1 tsp white sugar
1 medium red onion, halved & thinly sliced
1 large red or yellow bell pepper, seeded and thinly sliced
fresh cilantro, chopped, to serve
Cut the beef with the grain into 2-inch pieces, then thinly slice each piece against the grain.
In a medium bowl, stir together the beef, 1 tablespoon of soy sauce and the Sichuan pepper.
In a small bowl, stir together the remaining soy sauce, 2/3 of the neutral oil, chili-garlic sauce, garlic, vinegar, sesame oil and sugar.
In a 12-inch nonstick skillet over medium-high, heat 1/2 of the remaining neutral oil until barely smoking. Add half the beef in an even layer and cook without stirring until well browned, 1 to 2 minutes. Stir, scraping the pan, and cook, stirring, until no pink remains, 1 to 1½ minutes; transfer to a plate. Using the fat remaining in the pan, repeat with the remaining beef.
In the empty skillet over medium-high, heat the last of the neutral oil, until barely smoking. Add the onion and bell pepper, then cook, stirring occasionally, until the vegetables begin to soften, about 3 minutes.
Stir in the soy sauce mixture and any beef juices. Cook, stirring, until the liquid has thickened, about 1 minute.
Remove from the heat and stir in the beef. Transfer to a serving dish and sprinkle with cilantro.