In a mixing bowl, combine cornflour, table salt, ground black pepper, and Chinese five-spice until evenly mixed. Cut the skinless chicken thigh fillets into bite-sized pieces, then coat each piece thoroughly in the flour mixture.

In a large, deep skillet or wok, pour in vegetable oil and heat over medium-high heat until the oil begins to shimmer.

Carefully add the coated chicken pieces to the hot oil in batches, frying for about 5-7 minutes until they are golden brown and crispy.

Drain all but 1 tablespoon of oil from the skillet. Add chopped onion, red and green chillies, and minced garlic. Stir-fry for 2-3 minutes until the onions become translucent.

Toss the crispy chicken back into the pan with chopped spring onions and stir-fry everything together for an additional minute.