Mash the beans to a textured puree with a food processor or potato masher.
Transfer to a bowl and stir in the onion, chiles, cumin and salt. Using 1/4
cup of the bean mixture, make 3 x 1/2-inch patties.
Heat 2 tablespoons of the oil in a large heavy skillet. Put as many patties
in the skillet as will fit in a single uncrowded layer and fry over fairly high
heat until golden and toasted, about 1 minute per side. Transfer to a platter.
Fry remaining patties.
Sprinkle each patty with salsa, then drizzle Crema over.