Preheat the oven to 375°F (190°C). This ensures your casserole will bake perfectly.

Brown the ground beef in a large skillet over medium heat. As it cooks, break it apart with a spatula to ensure even browning. Once the beef is cooked through, drain any excess fat.

Sauté the onions with the beef. Add the diced onion to the skillet and cook until softened, about 3 minutes. This step adds a lovely, savory flavor to the meat.

Season the beef. Stir in the garlic powder, cumin, chili powder, salt, and pepper. Let the mixture simmer for another 2 minutes, allowing the spices to bloom and coat the meat evenly.

Layer the casserole. In a 9x13-inch baking dish, start with a layer of torn tortillas. Add a layer of the seasoned beef mixture on top, followed by a generous drizzle of enchilada sauce and a sprinkle of shredded cheese. Repeat this layering process until all ingredients are used, ending with a layer of cheese on top.

Bake. Cover the casserole with aluminum foil and bake for 20 minutes. After 20 minutes, remove the foil and bake for an additional 10 minutes or until the cheese is melted and bubbly.

Serve. Once out of the oven, let the casserole rest for a few minutes to set. Top with a dollop of sour cream and extra cilantro if desired.