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1
Heat the neutral oil in a wok or small saucepan to 160 °C. Add the raw cashews and deep-fry, stirring constantly, until they reach a pale gold — pull them at pale gold rather than waiting for full colour, because residual heat in the nut will carry them a shade darker on the paper. Lift out immediately with a slotted spoon and drain; the cashews are done when they are uniformly pale gold and smell of toasted nut.
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2
In the same oil at the same temperature, fry the dried chilli pieces for 20–30 seconds until crispy and a deeper, darker red, keeping them moving so no single piece sits against the bottom long enough to scorch and turn bitter. They must not blacken. Remove and drain alongside the cashews; the signal is colour: dark red, not black.
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3
Combine the oyster sauce, fish sauce, dark soy sauce, and palm sugar in a small bowl and stir until the sugar dissolves. Taste now, before anything else enters the wok, because the sauce sets the flavour of the entire dish and sweetness cannot be pulled back once the chicken is in. The sauce should be savoury-forward with restrained sweetness.
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4
Drain all but 2 tbsp of oil from the wok and set over high heat until smoking — a properly smoking wok sears the chicken rather than steaming it, keeping the pieces distinct and lightly coloured rather than pale and wet. Add the chicken and stir-fry, spreading pieces against the wok surface, for 3–4 minutes in total. The chicken is ready when all surfaces are opaque and cooked through with no pink remaining.
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5
Add the yellow onion wedges to the wok and toss with the chicken for 30–40 seconds, so the onion picks up the heat and the wok juices without surrendering its structure. Pour in the prepared sauce and toss to coat evenly. The onion should retain some resistance to the bite.
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6
Add the spring onion lengths and the fried cashews and dried chillies, then toss once or twice — no more — over high heat, because a cashew that lingers in a wet, steaming wok loses the crispness it took two separate fryings to build. The spring onion should be just wilted at the edges but still green and textured. Remove from heat immediately.