Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish.
In a skillet over medium heat, cook ground beef with diced onion until browned. Add garlic and cook 1 more minute. Drain excess grease.
Stir in taco seasoning, enchilada sauce, and green chiles. Simmer for 2–3 minutes until thickened slightly.
In the baking dish, spread a thin layer of beef sauce. Top with a layer of tortillas, more beef mixture, and cheese. Repeat layers, ending with cheese on top.
Cover with foil and bake for 20 minutes. Remove foil and bake an additional 10 minutes, until cheese is bubbly and lightly golden.
Let the casserole rest for 5–10 minutes before slicing. Top with sour cream, chopped cilantro, or green onions if desired.