Loofah and Chicken Stir-Fry

Stir together chicken, cornstarch, and 1 teaspoon sesame oil in a small bowl. Stir together oyster sauce, soy sauce, sugar, and stock in another bowl until sugar is dissolved. Remove ridges from loofah with a vegetable peeler, then scrape skin lightly with a sharp small knife (a little green skin should remain). Cut loofah lengthwise into 2- by 1/2-inch sticks. Heat peanut oil in a wok over moderate heat until it registers 350 °F on thermometer, then cook chicken, stirring, just until no longer pink, about 11/2 minutes. Transfer to a bowl with a slotted spoon, then pour oil into a heatproof container and reserve. Heat wok over high heat until a bead of water dropped onto cooking surface evaporates immediately. Add 3 tablespoons reserved peanut oil, swirling wok to coat evenly, and heat until it just begins to smoke. Stir-fry mushrooms until lightly browned and tender, 1 to 2 minutes. Add beans, chiles, garlic, and ginger and stir-fry until fragrant, about 30 seconds. Add loofah and toss until well coated. Add stock mixture and bring to a boil. Add chicken and return sauce to a boil. Stir cornstarch mixture and add to sauce, then boil, stirring, until sauce thickens slightly and becomes translucent. Serve drizzled with remaining 1/4 teaspoon sesame oil. Also known as "ridged gourd" and "Chinese okra."