Heat 1 teaspoon of the oil in a skillet over medium heat. Add the diced onion and cook for 3–4 minutes, until softened, then stir in the garlic and cook for about 30 seconds.

Stir in the cooked rice, drained black beans, salsa, chili powder, cumin, and kosher salt. Cook uncovered for 4–5 minutes, stirring occasionally, until hot; lightly mash some beans if you want a more cohesive filling.

Warm the corn tortillas in a dry skillet, in the microwave, or wrapped in foil in a low oven. Heat them just until flexible so they fold without cracking.

Divide the rice-and-bean mixture among the eight tortillas, taking care not to overfill them. Top each taco with about 2 tablespoons of shredded cheese.

For soft tacos, fold and serve immediately. For crisp tacos, heat the remaining oil in a skillet over medium heat, fold the tacos in half, and cook for 2–3 minutes per side until golden and the cheese has melted.

Finish the tacos with tomato, lettuce or cabbage, cilantro, avocado, sour cream or yogurt, salsa, and hot sauce as desired. Serve with lime wedges for squeezing over each taco.