In a mixing bowl, combine cornflour, table salt, ground black pepper, and Chinese five-spice. Cut chicken thigh fillets into quarters and coat with the cornflour mixture.

In a large frying pan, pour in vegetable oil and heat over medium-high heat until it shimmers at about 180°C (350°F).

Add coated chicken pieces in batches to the hot oil, frying for about 5–7 minutes until golden. Transfer to a plate lined with paper towels.

Remove most oil from the pan, leaving about 1 tablespoon. Over medium heat, stir-fry sliced onion, red and green chillies, and minced garlic for about 2 minutes.

Add the crispy chicken back to the pan with stir-fried vegetables, tossing to combine. Fold in sliced spring onions and serve immediately.