Put the cornflour, rice wine, sugar, salt and black bean sauce in a large bowl and combine to make a smooth paste. Toss the pork into the bowl and stir to cover. Set aside for 10 minutes.
Heat 1 tablespoon of the groundnut oil in a wok over a high heat until the oil starts to shimmer. Add half the pork and stir-fry for 2–3 minutes until golden, then remove with a slotted spoon and set aside. Heat another 1 tablespoon of oil and stir-fry the rest of the pork in the same way.
Wipe the wok clean with a piece of kitchen paper and heat the remaining oil over a high heat. Add the onion, red pepper, ginger and garlic and stir-fry for 2 minutes. Return the pork to the wok with the measurement water and stir-fry for 1 minute.
Add the spring onions, chillies and sesame oil to the wok and cook for a further 30 seconds, then serve.