Put the pork belly in a large pot and cover with water. Bring to a boil over high heat and cook until it fork tender, 1 hour 30 minutes.
Place the pork in a strainer and drain to remove all of the water, 30 minutes.
Add the oil to a deep fryer or Dutch oven and heat to medium-high heat. Fry the pork until golden brown, 30 to 45 minutes. (The thicker the slab of belly, the longer it will take to fry.) Transfer to a paper towel-lined plate.
Chop the pork belly into 1-centimeter-square pieces. Toss the pork belly, onions, tomatoes, fish sauce and Hawaiian salt in a medium mixing bowl. Garnish with green onions.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Elena's Home of Finest Filipino Foods, Las Vegas, NV