Preheat oven to 350 F. Place the roasting rack in the middle of the oven.
Clean pork belly slab and pat dry with paper towels.
Place the meat onto a flat surface and rub the skin with 1/2 tablespoon of onion and garlic powder and rub the rest into the inner belly meat.
Lay the belly slab with skin on the flat surface.
Put all the garlic, red onion, green onion, bay leave at the long end of the belly and roll the slab to form a tube and tie with kitchen twine.
Rub oil on the meat.
Arrange pork belly in the middle of the roasting pan and bake belly for four hours.
After four hours, remove belly from the oven and trasfer the oven rack to the lowest level. Broil the pork belly for fifteen minutes. Keep an eye of the meat since it will burn quickly. Keep on checking the oven.
Let the belly sit for another 30 minutes before serving.