Preheat oven to 165°C/325°F. Season pork belly with salt and pepper.
Place oven bag in large baking dish. Lay chopped ginger, garlic and onion in the bag and place pork on top. Pour cider into bag. If necessary, add a little water to bring the level of fluid in the bottom of the bag up to 1cm and seal. Pierce a couple of holes in the top of bag and cover tightly with foil. Bake approximately 3 hours until the pork is very tender but not falling apart. Pork can be enjoyed as it is at this point or carry on for skewer version…
For the pork skewers, allow pork to cool in fridge overnight, before using a sharp knife to cut into desired size pieces – approximately 3cm/1in.
For sauce, whisk together all ingredients and cover until needed.
To assemble, place 2 pieces of pork on skewer with spring onion in between. Dip skewers into sauce and grill each side while basting with sauce until hot through and glazed – approximately 10 minutes.