Heat the oil in a wide saucepan that has a lid, then brown the pork in batches and set aside in a bowl.
Add the onions to the pan with a splash of water and some more oil if it’s looking too dry. Cook gently for 10-15 minutes until very soft and starting to brown at the edges. Add the garlic, oregano and cumin and cook for a couple of minutes, then throw in the tomatoes and let them break down on a moderate heat for 5-10 minutes before returning the pork and any juices to the pan.
Stir through a good few pinches of salt and some grinds of black pepper. Cover with the lid and cook gently for 1 to 1 1/2 hours until the pork is tender.
Once the meat is tender, stir in the corn kernels and the cob pieces and cook, without the lid, for another 5-10 minutes until the corn is done.
Taste for seasoning: if your tomatoes were quite acidic, you may need to add a little sugar to balance them. Serve garnished with some chopped coriander and a few chilli slices.