Cut the pork belly into two pieces if it's too long. If using shorter, thicker pieces, leave them as is.

Heat a pan or wok over high heat and sear the pork belly on all sides until golden brown.

Remove the seared pork belly and clean the pan with a paper towel, or use a new pan.

In the pan, combine soy sauce, mirin, sugar, and water. Add the halved onion, chopped green onion, and bay leaves.

Bring the sauce to a boil, then add the seared pork belly. Cook on high heat for 20-25 minutes.

Reduce the heat to medium and simmer for about 90 minutes, or until the sauce is reduced and thickened.

Remove the pork belly and let it cool slightly. Discard the onion, green onion, and bay leaves from the sauce.

Slice the remaining half onion into thin strips and cook it in the reduced sauce until tender.

Slice the pork belly into bite-sized pieces.