Serves three or four people.
Chop the onion fairly coarsely, and fry in oil or butter until slightly soft - about 5 minutes.
Put about half a pint of tomato puree in a pan, and add the oil, chili and cumin. Chop the garlic and add that. Heat it up and simmer it for a few minutes.
I have been using Old El Paso "Soft Corn Tortillas", which are easy to get from supermarkets. Unfortunately they're not the real thing; they're only about 30% corn, and don't really taste of corn. Never mind...
Wet a tortilla under the tap, and microwave it on full for 20 seconds, to soften it. Spoon a quarter of the onions onto the tortilla, and a matching quantity of refried beans. Roll it up, and put it in an ovenproof dish. Repeat for the remaining tortillas.
Pour the tomato sauce over the rolled-up tortillas. Cover with grated cheese. Grill until the cheese has melted and the tortillas are hot through.
Serve with a dollop of sour cream, or some salsa cruda, or guacamole, or some spanish rice, or all of these, or something else.
I usually use tinned Old El Paso refried beans, from the supermarket. The above instructions will use up a tinful. You can make your own refried beans: soak and cook half a cupful of Pinto beans until they are tender, then mash them up with a big knob of butter and two or three chopped garlic cloves.