1pound boneless, skinless chicken thighs or breasts, thinly sliced across the grain into bite-size strips
½teaspoon crushed red pepper flakes
3tablespoons soy sauce, divided
2tablespoons seasoned rice vinegar
2tablespoons Shaoxing wine (Chinese rice wine) or dry sherry
2tablespoons vegetable oil, divided
6scallions, ends trimmed, cut into 1-inch pieces on the diagonal
12-inch piece ginger, peeled, thinly sliced crosswise
12ounces green beans, trimmed, halved crosswise (about 4 cups)
Steamed white rice, chopped toasted cashews or peanuts, sesame seeds, and/or thinly sliced fresh chiles (for serving; optional)
Toss chicken, cornstarch, red pepper flakes, a pinch of salt, and 1 Tbsp. soy sauce in a medium bowl. Stir vinegar, wine, and remaining 2 Tbsp. soy sauce in a small bowl. Have all your other ingredients prepped and ready to go (once you start cooking, there isn’t a stopping point and you’ll need them handy)
Heat 1 Tbsp. oil in a large skillet (not nonstick) over high. When oil is shimmering and slides quickly across surface of pan, add scallions and ginger and cook, tossing, until scallions are browned and softened, about 2 minutes. Add green beans and a pinch of salt and cook, tossing often, until green beans are crisp-tender, about 4 minutes. Transfer green bean mixture to another medium bowl.
Heat remaining 1 Tbsp. oil in same skillet over high. When oil is shimmering again, add chicken mixture and arrange slices in a single layer in skillet. Cook, undisturbed, until chicken is browned and caramelized on first side, about 1 minute. Toss and continue to cook until meat is no longer pink and cooked through, about a minute or two longer. Pour in wine mixture and green bean mixture and cook, tossing briskly, until sauce is thickened and all ingredients are coated, about 30 seconds. Remove from heat and taste, then season with more salt, if desired.
Divide stir-fry among plates. Serve with rice alongside, if using. Sprinkle with desired toppings.