Steam in a bamboo steamer, covered, over a wok of boiling water for 30 minutes.
Remove and whilst the belly is still hot, lightly score the skin at 1cm intervals using a sharp knife, then rub salt into the score marks.
Place the belly on foil, folding the sides up to the skin, leaving the skin uncovered.
Place into a deep tray; add water until the belly is half submerged.
Roast for 30 minutes at 240°C (fan)/ 465° F or until the skin is crisp and crackling.
Once cooked, cut the crackling away from the belly and scrape off any remaining fat.
Cut into strips and set aside.
Slice the belly into 1cm (1/3 inch) slices and keep warm until ready to use.
Black pepper caramel
Place the palm sugar into a saucepan with 50 ml (1 ⅔ floz) water and cook over medium-high heat until the sugar has melted and the caramel starts to bubble.
Add the shallots and garlic, then just before the caramel starts to burn, add the vinegar, fish sauce and pepper to stop the cooking process.
Bring back to the boil and simmer for 1-2 minutes to reduce a little, then remove from the heat and set aside.
The caramel should be thick but of a pouring consistency just a bit thicker than honey.
Tuna
Coat the tuna loin in chili salt and sear evenly all over in a lightly oiled hot pan.
Remove from pan and sat aside to cool.
Slice into 1cm (1/3 inch) thick pieces.
To Serve
Assemble layers of pork belly, grapefruit and tuna.