Heat the lard or vegetable oil in a large frying pan, add the onion and cook for 5–10 minutes until golden. Add the garlic and cook for a further 1 minute.
Meanwhile, place the black beans and 2 tablespoons of the reserved bean liquid in a food processor or blender and whizz until smooth.
Add the puréed beans and oregano to the onion mixture, reduce the heat to low and cook for 5 minutes, stirring frequently. Add 100 ml (3½ fl oz) of the reserved bean liquid and cook for a further 5 minutes until the beans are the consistency of very soft mashed potatoes.
Season, sprinkle over the cheese and serve garnished with the coriander and chilli.