Heat 1 tablespoon olive oil in a large skillet over medium heat. Add diced onion and cook for 3-4 minutes until translucent and softened. Add minced garlic and stir constantly for 1 minute to prevent burning while releasing its aroma.

Add ground beef to the skillet, breaking it apart with a spatula. Cook for 5-7 minutes until completely browned with no pink remaining. If using ground beef with 20% fat or higher, drain excess fat, leaving about 1 tablespoon for flavor.

Stir in black beans, diced tomatoes with green chilies, and taco seasoning. Let the mixture simmer for 5 minutes to allow flavors to blend. The mixture should be thick enough to coat the back of a spoon. Season with salt and pepper to taste.

While the beef mixture simmers, preheat your oven to 350°F (175°C). At the same time, bring a large pot of salted water to a rolling boil. Add cheese tortellini and cook for 3-5 minutes until they float to the surface. Drain and set aside.

In a large mixing bowl, combine the cooked tortellini with the beef mixture, folding gently to coat evenly without breaking the pasta.

Spread a thin layer of enchilada sauce on the bottom of a 9x13 inch baking dish. Transfer the tortellini-beef mixture to the dish, spreading evenly.

Pour remaining enchilada sauce over the top of the mixture, ensuring it's well covered. Evenly distribute all 2 cups of shredded cheddar cheese over the top, ensuring complete coverage.

Cover the baking dish with aluminum foil and bake for 20 minutes. Remove foil and bake for an additional 10-15 minutes until cheese is melted, bubbly, and lightly golden at the edges.

Remove from oven and let cool for 5 minutes. This allows the sauce to set slightly, making it easier to serve without falling apart. Garnish with fresh cilantro and serve with sour cream if desired.