Cut the pork belly into 2-inch pieces, making sure each piece has both meat and fat. Season the pork pieces evenly with salt, rubbing the salt all over.
Heat a thick-bottomed pan over high heat. When hot, place the pork pieces in the pan in a single layer, making sure not to overcrowd them.
Cook for about 7-10 minutes, turning the pieces occasionally, until you see fat starting to come out from the pork. You'll notice clear oil beginning to collect in the pan.
Once you see enough oil in the pan, turn the heat down to its lowest setting. Cover the pan and let the pork cook slowly for about 45-50 minutes. Every 10-15 minutes, lift the lid and turn the pieces so they brown evenly.
Keep cooking until the pork turns deep golden brown and the pieces have become smaller and crispier. You can test a piece - it should be crunchy outside but still juicy inside.
Using a slotted spoon, transfer the crispy pork to a wire rack placed over a tray. Let it rest for 5 minutes - this helps make it even crispier.
Serve hot with spicy vinegar for dipping. For the vinegar dip, simply mix vinegar with chopped chilies, minced garlic, and a pinch of salt and pepper.
Keep the pork fat that's left in the pan - it's perfect for cooking other dishes!