In a small bowl, mix 1 teaspoon each of salt, pepper, garlic powder and onion powder. Sprinkle over the meat side of the belly and rub well. Arrange lemongrass and green onions in the middle (fold to fit the length of the meat) and roll the belly until it reaches both ends. Tuck the greens inside the meat to prevent burning. With a kitchen twine, make tight knots about an inch apart to keep the rolled shape intact. Wipe the rolled meat with paper towels.
Rub the skin with 2 teaspoons of sea salt and let it rest for 20-30 minutes. This will draw out the extra moisture from the meat. Wipe the pork skin once again with paper towels to remove all visible moisture. Place the rolled pork on top of the rack fitted in a roasting pan, seam side down.
Preheat the oven to 300F. When ready, pat the skin one more time with paper towels before putting it in the oven. Bake for 2 hours. Then, increase the temperature to 350F. After 1 hour, baste the skin with the oil drippings, rotate and continue cooking for 1 more hour (2 hours total at 350F). This will ensure even browning of the roast.
Baste again with oil then crank the oven temperature to 425-450F (**see notes) and roast until golden and crispy (crackling skin). It will take about 20-30 minutes.
Let the bellychon rest for 15 minutes before chopping. This will ensure the meat juices redistribute, making the roast very juicy. Serve with Mang Tomas lechon sauce or soy-vinegar dip with lots of chilies.
Notes
*If you don’t have a roasting pan, place the rolled meat directly on the oven rack (middle) then position a rimmed baking sheet under (lower oven rack) to catch all the meat drippings.**Oven temperatures vary. Start at 450F but if it’s browning too quickly, reduce to 425F.