Asian Shredded Chicken

Bring 1 1/2 inches water to a boil with ginger in a deep 12-inch skillet and add chicken. Poach at a bare simmer, turning over once, until just cooked through, 8 to 12 minutes. Transfer chicken with a slotted spoon to a plate and when cool enough to handle, finely shred. Whisk together soy sauce, vinegar, red pepper flakes, and sesame oil in a large bowl to make dressing. Heat vegetable oil in cleaned skillet until hot but not smoking, then sauté mushrooms over moderately high heat, stirring, until golden, about 6 minutes. Add scallions, garlic, and salt and pepper to taste and sauté, stirring, until scallions are just softened, about 1 minute. Add to dressing, then add chicken and cilantro and toss. Serve chicken salad with lettuce.