Cook the Beef. In a large skillet, heat olive oil over medium heat. Add diced onions and cook until softened, about 2-3 minutes. Stir in minced garlic and cook for another minute. Add ground beef and cook until browned, breaking it up into small crumbles as it cooks.
Season the Filling. Once the beef is browned, stir in taco seasoning and black beans (or pinto beans). Add a small amount of water and let the mixture simmer for 5-7 minutes until well combined. Remove from heat.
Fill the Tortillas. Preheat your oven to 350°F. Spread a thin layer of enchilada sauce at the bottom of a greased 9x13-inch baking dish. Place a tortilla on a flat surface, spoon 2-3 tablespoons of the beef and bean mixture into the center, sprinkle with cheese, and roll it up tightly. Place the rolled enchilada seam-side down in the baking dish.
Top with Sauce and Cheese. Repeat with the remaining tortillas. Pour the remaining enchilada sauce over the top of the rolled enchiladas, making sure to cover them evenly. Sprinkle the remaining shredded cheese over the top.
Bake. Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the cheese is melted and bubbly. If you like the cheese extra crispy, broil the enchiladas for the last 2-3 minutes.
Serve. Remove from the oven and let cool for a few minutes before serving. Garnish with fresh cilantro, sour cream, or sliced jalapeños for extra flavor.