Make 3 lemon peels from the Lemon (1).
Pulse Salt (2 tablespoon), Granulated Sugar (1/2 tablespoon), lemon peels, Bay Leaf (3), Black Peppercorns (1 teaspoon) and White Peppercorns (1 teaspoon) in a spice grinder or blender until coarsely ground.
Place the slab of Skin-On Pork Belly (1 piece) in a baking-sheet. Pork belly should be roughly 8 × 8-inches (can be a square or rectangle). Rub the salt-mixture evenly on all sides of the pork belly.
Let sit in the fridge for 2 hours. In the last 30 min, preheat the oven on 300 degrees F (150 degrees C).
Rinse off all the salt-mixture from the pork-belly and the baking-sheet, then place the belly back into the sheet skin-side down (to keep the skin layer relatively flat).
Cover tightly with foil then roast in the preheated oven for 2 to 2:15 hours. The meat should be tender that a small knife can be easily inserted, but not falling apart.
Remove the sheet from the oven and let cool for 30 min, then chill in the fridge for 1 hour (skin-side down still) until firm (for easy trimming). Everything up till now can be prepared the day ahead.
30 minutes before serving, carefully remove the pork-belly from the baking-sheet.
Look at the cut-side and get familiar with the anatomy of the belly. The skin is a very obviously translucent and darker layer apart from the white, opaque fat-layer underneath.
Then grab a big handful of wooden or metal skewers, evenly and thoroughly, make tiny punctures through the skin down the top layer of fat. Instead of random jabbing, move systematically from left to right/top to bottom.
Now trim off irregular edges so you have a 90º brick all around. This helps the belly brown more evenly and beautifully.
Heat a non-stick skillet over medium-high heat, then place the belly skin-side down in the center of the skillet.
Cover with a piece of foil just big enough to leave steam-holes around the edges (this prevents splattering as well as warming the belly as it cooks). Once you hear sizzling sounds, turn the heat down to LOW.
If your pork-belly does not have a flat and levelled skin-surface, you can apply weight (I used a small cast-iron skillet) where it needs it for the first 10 min.
We want the entire layer of skin to be thoroughly blistered without burning, this take no less than 15 min, up to 20 min. You can check by uncovering the foil and look if the entire thickness of the skin-layer is blistered through.
Place the belly skin-down down, then with a sharp knife, cut through the meat part by zig-zaging the knife, then once you get to the skin, simply press the knife down with swift and firm pressure. Cut the belly into small cubes.
Serve with yellow Yellow Mustard (to taste), or on rice drizzled with Sweet Soy Sauce (to taste).