In a small bowl, whisk together the Chinese five spice, salt, and garlic powder. Then flip your pork belly meat side up and skin side down and rub the dry seasoning into the meaty side only.
Flip the pork belly strip skin side up and clean off the skin as much as possible with a clean dry towel. Then dry it the skin off with another piece of paper towel.
Next poke as MANY holes as you can into the skin and use a lot of pressure. This is the key to a successful Chinese roast pork belly crackling. (I would even suggest investing in the tool I used below which is also a meat tenderizer so it is dual purpose. This will make the process SOOO much easier. It is only $13 on amazon. If you cannot budget for this tool, use a sharp metal cooking needle.)
Then per each pork belly strip, wrap aluminum foil around the base and the sides of the pork leaving the skin open and uncovered. Do not create a tall edge with your foil. Create a short edge enough that you can pick up the sides. If you create tall edge the oven heat will not reach the skin evenly, resulting in a non crispy skin.
After wrapping the pork belly in foil, dry it again with a clean towel.
Brush a light coat of white vinegar. You are not drenching it in vinegar. The vinegar helps to remove moisture believe it or not.
Then evenly and lightly sprinkle sea salt over top. This is the layer that you will taste first so do not over salt either.
Bake at 225 degrees F for 60 minutes. Your skin will not puff up here so do not worry if you do not see it crackle. This is normal!
Then remove from the oven and evenly brush a thin coat of oil onto the skin of each strip.
Then bake again at 400 degrees F for 40 minutes. This is when you will see the skin puff up and crackle. Monitor this process around the 35-minute mark and check for golden crispy crackled skin. If you still do not see it keep it in the oven for 40 minutes and if you still do not see it keep baking until you do. The pork belly is a very forgiving cut of meat and will stay moist thanks to all the fat.
Once you see the crackled puffy skin, remove from the oven, and LET IT REST for 10 minutes so the juices go back into the meat. You can leave it in the foil or remove it and place it on your chopping board.
When chopping, flip it over so it is skin side down. Holding the pork strip firm with your dominant hand and with A VERY SHARP heavy knife like a butcher knife, slice the meat down firmly. Then pause before you reach the skin, and with TWO HANDS slice down. This ensures a smooth slice.