Ingredients

• 1 1/2 pounds skinless boneless chicken breasts (4 halves), cut crosswise into 1/4-inch-thick slices
• 2 tablespoons water
• 2 tablespoons rice vinegar (not seasoned)
• 2 tablespoons soy sauce
• 2 teaspoons sugar
• 1/2 teaspoon dried hot red pepper flakes
• 3 tablespoons vegetable oil
• 1 large onion, halved lengthwise, then thinly sliced lengthwise
• 3/4 pound fresh shiitake mushrooms, stems discarded and caps quartered
• 1 1/4 cups frozen peas, thawed
• 2 tablespoons sesame seeds, toasted
• Accompaniment: steamed rice

Instructions

1. Pat chicken dry and season with salt.
2. Stir together water, vinegar, soy sauce, sugar, and red pepper flakes in a small bowl until sugar is dissolved.
3. Heat a wok or 12-inch skillet over high heat until a bead of water dropped onto cooking surface evaporates immediately. Add 1 tablespoon oil, swirling wok to coat evenly, and heat until hot and just smoking. Add onion and stir-fry until golden and crisp-tender, about 2 minutes. Transfer onion to a large bowl.
4. Add 1/2 tablespoon oil to wok and heat until just smoking, then stir-fry half of chicken until just cooked through, about 1 1/2 minutes. Transfer to bowl with onion and stir-fry remaining chicken in 1/2 tablespoon oil in same manner, transferring to bowl.
5. Add remaining tablespoon oil to wok and heat until just smoking, then stir-fry mushrooms until just tender, 3 to 4 minutes. Add peas and stir-fry until heated through, about 1 minute, then transfer to bowl.
6. Add vinegar mixture and sesame seeds to wok and, when liquid just reaches a boil, add chicken mixture and stir-fry until heated through, about 1 minute. Season with salt and pepper and serve over rice.