Mix the mince, chillies, half the spring onions and 1tbsp soy sauce together in a bowl. Shape into 12 even-sized meatballs with wet hands.
Heat 1 tbsp oil in a large frying pan and fry the meatballs until brown all over (you may need to do this in 2 batches). Transfer to a plate lined with kitchen paper.
Add a third of the stock to the pan and heat until it simmers, stirring with a wooden spoon to shift any meat stuck to the pan.
Return the meatballs to the pan with the rest of the stock, the remaining soy sauce, sweet chilli sauce and vinegar.
Bring back to the boil, reduce the heat and partially cover. Simmer gently for 5 minutes.
Add the cornflour paste and heat for a further 5 minutes, or until the sauce thickens. Cook the rice according to packet instructions and steam or lightly boil the boil the pak choi. Serve with the meatballs.