The night before you plan to make these, score the skin: use a serrated knife to make crossways cuts through the skin (do NOT cut through the meat) about 1" apart. Rub the meaty of the pork belly (not the skin) with blackening seasoning. Dry the skin with a paper tower. Place in fridge uncovered.
An hour before cooking, remove from fridge.
Preheat an oven to 425F. Pat the skin dry with paper towel again. Place on a wire rack set inside a baking tray (lined with foil for easier cleanup).
Transfer to oven and roast for 30 minutes. Reduce oven heat to 350, sprinkle skin with blackening seasoning. Cook for an additional 30 minutes.
Remove from oven and let rest for 15 minutes.
While the pork is resting, make the slaw. Peel the mango and finely chop. Add it to a bowl large enough to toss the slaw in, and mash with a fork. Add the pineapple juice and apple cider vinegar; stir to combine. Add the slaw mix and toss until evenly combined.
Slice the pork into 1/2" slices. To assemble: Place 2 slices of pork on a potato bun, Top with 2 slices of fresh pineapple and a pile of slaw. Add a couple sprigs of cilantro and top with the other bun.