Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
In a large skillet over medium-high heat, brown the ground beef and diced red onions until the meat is fully cooked and the onions are softened. Drain off any excess fat.
Stir the drained black beans and 1/2 cup of the red enchilada sauce into the skillet with the beef. Simmer for 2 to 3 minutes until heated through.
Warm the tortillas to make them pliable. Spoon approximately 1/3 cup of the beef and black bean filling down the center of each tortilla, sprinkle with a pinch of cheddar cheese, and roll tightly.
Spread 1/2 cup of red enchilada sauce across the bottom of the prepared baking dish. Place the rolled enchiladas seam-side down in a single layer.
Pour the remaining 1 cup of enchilada sauce evenly over the top of the rolled tortillas and sprinkle generously with the remaining shredded cheddar cheese.
Bake uncovered for 20 to 25 minutes, or until the sauce is bubbly and the cheese is fully melted.
Remove from the oven and let rest for 5 minutes. Garnish with chopped cilantro, and serve warm with guacamole and fresh lime wedges.