In a small bowl, combine the beans, onion, cumin, chili powder, and salt. Mash the ingredients together with a fork. (If you are a fan of cilantro, you can mix in 2 tablespoons, chopped.) Set aside along with the cheese.
Heat 1 teaspoon of the oil in a small (7-inch diameter works well), nonstick or cast-iron skillet over medium-high heat. Add 1 tortilla and allow it to cook for about 30 seconds to start the crisping process. Remove from the heat long enough to spread 1/4 cup of the bean mixture over one half of the tortilla. Then sprinkle 2 tablespoons of the cheese evenly over the beans, and return to the heat.
Using a spatula, carefully fold the unfilled half of the tortilla over the bean-filled half to form a taco-like shell. Press down lightly on the tortilla, and don’t worry if some of the filling oozes out. Just let it sear in the pan and eat alongside your taco or tuck it back in later. Let the taco cook until it is nicely browned and crispy, approximately 3 minutes per side. (As a precaution, peek underneath before 3 minutes is up to avoid burning.) Remove to a plate and serve with toppings of choice.
The cooked tacos may be placed on a baking sheet in a 200 degree F oven or toaster oven to keep warm while preparing the remaining tacos. The filling may also be stored in the refrigerator and used, one or two tacos at a time.