Preheat the oven to 180°C. Spread the cashews onto a baking tray and roast for 8–10 minutes, stirring halfway, until deep golden brown and fragrant. Set aside to cool.
In a bowl, combine the chicken with the dark soy sauce and oyster sauce. Marinate for 15 minutes. Whisk together all the sauce ingredients in a small bowl and set aside.
Heat the avocado oil in a large wok or frying pan over high heat. Cook the chicken in 2 batches for 4–5 minutes, until browned and almost cooked through. Remove from the pan and set aside.
If needed, add a little more oil. Add the onion and stir-fry for 2 minutes. Add the capsicums and cook for another 2–3 minutes until tender-crisp. Stir in the garlic and dried chilies and cook for 30–60 seconds until fragrant.
Return the chicken to the pan and pour in the sauce. Toss everything together for 1–2 minutes until the sauce thickens slightly and evenly coats the chicken. Stir through the roasted cashews and green onions. Remove from the heat and serve immediately over steamed jasmine rice.
