Use to fill tortillas, adding grated cheese, chopped fresh vegetables and salsa to taste...
Heat the oil and add the onion, garlic, cumin, coriander, and chili if used. Stir fry 2 minutes. Add the beans and stir until everything is heated through. Mash some of the beans if you wish.
Source: Cooking With Stones by Hilary Howard and Julia Stapleton
Note: I usually fry the onion until it is soft and cooked through. If you fry it for only 2 minutes, it tends to stay undercooked and a bit too strong in flavour.