Toss together chicken, wine, 1 tablespoon soy sauce, Chinese five-spice, and garlic in a large bowl. Cover and refrigerate at least 20 minutes or up to 5 hours.
Sprinkle chicken with 1/3 cup cornstarch; toss to coat. Place chicken pieces in a single layer on a large plate; set aside.
Heat 1/4 cup oil in a large wok or stainless steel skillet over medium. Add cashews, and cook, stirring constantly, until lightly toasted, about 2 minutes. Add chiles, and cook, stirring constantly, 1 minute. Remove from heat. Transfer cashew mixture to a large heatproof bowl using a slotted spoon or spider, reserving oil in wok.
Place wok over high heat. Working in 2 batches, add chicken in an even layer, and cook, flipping once, until chicken is deeply browned and cooked through, 2 to 3 minutes per side, adjusting heat if needed to prevent overbrowning. Transfer chicken to bowl with cashews. Meanwhile, whisk together 2 tablespoons water and remaining 1/2 teaspoon cornstarch in a small bowl until smooth; whisk in oyster sauce, brown sugar, and remaining 1 tablespoon soy sauce until sugar is dissolved. Set aside.
Add scallions, onion, and remaining 1 1/2 teaspoons oil to wok; cook over medium-high, stirring often, until onion is crisp-tender, about 4 minutes. Return chicken and cashew mixture to wok; add oyster sauce mixture. Cook over medium-high, stirring constantly and scraping bottom of wok to loosen any browned bits, until sauce thickens slightly and glazes chicken, 20 seconds to 1 minute. Remove from heat; serve immediately with rice.
