heat the oil in a heavy based saucepan. add onions, cumin and coriander and cook over a low heat for half an hour or until the onions soften and caramelise.
add the beans, stir and mash the mixture. stir in the garlic, chili flakes and vegetable stock. cook, stirring frequently, until the paste thickens.
season with salt and serve with the coriander.