Step by step

Leave to marinate for an hour, then fry in oil and leave to cool

If you find it hard to digest onion, leave it in some milk for half an hour before using: it will become sweeter and more delicate, and above all much more digestible.
In China there is a dish similar to this one called Gwa-bao, and is also a ‘bun’ filled with pork. The difference is that the pork in this case is not steamed but rather fried. The Gwa-bao are "cousins" of Mantou, common steamed dumplings and meat, which are also very popular in China.