Preheat oven to 350 degrees F, and spray a 9x13” casserole dish with cooking spray.
In a large skillet, cook the ground beef and onions over medium heat until the beef is no longer pink and the onions are tender. Drain well and return to the pan.
Stir in taco seasoning, diced green chilis, and minced garlic. Cook for 5 minutes longer.
Assemble the casserole. Pour just enough enchilada sauce (about ⅓ cup) into the prepared casserole dish to coat the bottom of the baking dish.
Layer the corn tortillas over the sauce. It may help to cut the tortillas in half.
Top the tortillas with half of the beef mixture, more enchilada sauce (about ¾ cup), then ½ c. shredded cheese.
Repeat the layers: tortillas, the remaining beef mixture, ¾ c. enchilada sauce (reserving a bit for the top), and ½ c. shredded cheese.
Finally, top the layers with more tortillas, the remaining enchilada sauce, and the remaining cheese.
Cover the casserole with aluminum foil, and bake in a 350 degree F oven for 25-30 minutes. Remove foil and continue to bake for 10 minutes until the dish is bubbly and the cheese is melted.
Remove from oven and allow the casserole to cool for 5 minutes. Garnish with cilantro and enjoy!