Smear the ribs with the marinade ingredients mixed together in a bowl. Cover the bowl with cling film and leave to marinate in the fridge for at least 24 hours (the longer the better).
Preheat the oven to 190C/375F/Gas 5. Transfer the marinated ribs to a baking or roasting tin and cook for 30 mins, basting as they are cooking.
Turn the oven down to 160C/325F/Gas 3, cover the tray with foil and continue cooking and basting for another hour, then remove the foil and cook, basting regularly, for a further 30-45 minutes.
Remove the ribs from the oven, cover and keep warm until ready to serve.
For the stuffed onions, preheat the oven to 200C/400F/Gas 6.
Wrap the onions in foil, stand them on a baking tray and bake for about 45-50 minutes, or until they are fairly soft. Remove from the oven, take off the foil and leave to cool a little.
Meanwhile, prepare the stuffing. Melt the butter in a frying pan. Season the pork with salt, pepper and ground cumin, add to the pan and fry over a medium heat for a few minutes, stirring, until lightly coloured. Add 125ml/4½fl oz water and simmer gently for about 10 minutes or until the water has evaporated. Transfer to a bowl and leave to cool.
Once the onions are cool enough to handle, chop about 1cm/½in off the top of each, then carefully remove the skins, keeping the onions intact. Scoop out the centre of each onion with a spoon, leaving a couple of layers of flesh to hold them together. Reserve both the onion tops and scooped flesh.
Finely chop the scooped onion flesh and mix it together with the pork, breadcrumbs and parsley. Season to taste. Spoon the filling into the onions and replace the tops. Place on a baking tray, brush with oil and bake for about 15-20 minutes, until the onions are lightly-coloured and the filling is hot.