Place the duck in bowl with the garlic, hoisin, vinegar, rice wine, soy sauce, sugar, chilli, Chinese five-spice powder and salt. Mix well to combine, then marinate, covered, in the refrigerator for 30 minutes.
Heat half the groundnut oil in a wok over a high heat until the oil starts to shimmer. Toss in half the duck with its marinade and stir-fry for 3 minutes, until cooked, yet still slightly pink in the centre. Use a slotted spoon to remove the duck from the pan, to drain away any excess fat and wipe the wok clean with kitchen paper. Heat the remaining oil and stir-fry the rest of the duck in the same way.
Serve the duck topped with a scattering of cucumber and spring onion strips.