Cut the chicken into 1-inch cubes. Combine with the marinade ingredients, adding the arrowroot last. Marinate the chicken for 25 minutes.
While the chicken is marinating, prepare the vegetables and sauce: In a small bowl, combine the dark soy sauce, rice wine, and honey. Set aside.
Heat the wok over medium-high to high heat. Add 2 tablespoons oil. When the oil is hot, add the chicken. Stir-fry until it turns white but still slightly pink in the center. Remove from the wok.
Add 2 tablespoons oil. When the oil is hot, add the garlic and stir-fry until aromatic (about 30 seconds). Add the vegetables, red pepper flakes and the Szechuan peppercorns if using. Stir-fry briskly until the vegetables are tender-crisp, about 2 minutes.
Add the sauce to the wok. Bring to a boil. Add the chicken back into the pan. Stir in the cashews and the green onion, and continue stir-frying until the chicken is completely cooked through, another 30 seconds or so. Remove from the heat and stir in the sesame oil. Serve hot.