Lay the tortillas on a baking sheet and rub with oil. Grill on high for 1 minute on each side.
In a non-stick frying pan, fry your chorizo in the butter until a bit crisp. Add onion and garlic and fry until golden. Add spices, fry momentarily then add black beans. Add a little water if too dry. Mash with a fork as you fry. You want a nice chunky rough paste. Taste for seasoning.
Smooth the mix over the tostada. Top with fried egg and additional accoutrements. Destroy!