Preheat oven to 400°F. Grease a 9 x 13-inch baking dish; set aside.
In a large skillet or Dutch oven over medium-high heat, cook ground beef and onion until the meat is no longer pink. Add the garlic and cook for 1 more minute. Drain off the excess fat.
Stir in salsa, taco seasoning, beans, corn, enchilada sauce, and chiles.
Spread about 1 cup of the meat mixture in the bottom of the prepared baking dish. Top with a layer of 4 tortillas (overlapping is fine), 1/3 of the remaining meat mixture, and 1 cup of cheese.
Repeat with another layer of tortillas, another 1/3 of the remaining meat mixture, and another 1 cup of cheese.
Finally, add another layer of tortillas, the remaining meat mixture, and the remaining 1 cup of cheese. Cover the dish with aluminum foil.
Bake the casserole, covered, for about 15 minutes. Remove the cover and bake for 10-15 more minutes, until the filling is hot and bubbly and the cheese is melted on top.
Let stand for 10-15 minutes. Slice and serve. Garnish with optional toppings.