In a deep pan, put 3/4 L of water or just until the pork belly can be submerged into.
Turn the stove on in a medium hight heat, and put the pork belly.
Add in salt, pepper, onion, and garlic.
Let it boil for 30 mins or just until the pork belly is tender.
After boiling, take the pork belly out of the pan and pat it dry.
Cut the pork belly into medium thin slices.
Preheat a deep pan with the cooking oil. Then, deep fry the sliced pork bellies until golden brown.
For the sauce, just mix vinegar, soy sauce, sugar, and chilli flakes in a saucer.
Serve with rice!