Heat the olive oil in a large frying pan or skillet over medium-high heat. Add the sliced beef and cook until browned, about 3-4 minutes. Remove the beef from the pan and set aside.

Reduce the heat to medium and add the diced onion to the pan. Cook until the onion is translucent, about 3-4 minutes. Add the minced garlic and cook for an additional minute.

Add the cumin, chili powder, paprika, and cayenne pepper (if using) to the pan and cook for 1-2 minutes, stirring constantly, until fragrant.

Add the black beans to the pan and stir to combine with the onion and spice mixture. Cook for 2-3 minutes, until the beans are heated through.

Add the cooked beef back into the pan and stir to combine with the black bean mixture. Cook for an additional 2-3 minutes, until the beef is heated through.

Warm the corn tortillas by wrapping them in a damp paper towel and microwaving for 20-30 seconds. Assemble the tacos by spooning the beef and black bean mixture onto a tortilla, followed by a sprinkle of shredded cheese and any desired toppings.

Repeat the assembly process with the remaining ingredients and serve immediately. Alternatively, cook the beef and black bean mixture in advance and reheat as needed for meal prep.

To store leftovers, let the cooked mixture cool completely before transferring it to an airtight container. Store in the refrigerator for up to 3-5 days or freeze for up to 2 months. Reheat as needed.