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.