Heat the oil in a large frying pan, and add the onion and garlic. Cook over a medium-low heat for 5 minutes, until soft and translucent but not coloured.
Add the spices, and cook for a further 1 minute, stirring constantly.
Add the drained tins of black beans, and turn the heat up to medium-high. Cook for around 5 more minutes, stirring regularly, until the beans are very soft (if the mixture looks too dry, just add a splash of water). Coarsely mash the beans with a potato masher or the back of a fork.
Season to taste, and serve garnished with fresh coriander.