01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with cooking spray or oil.
02 - In a large skillet over medium-high heat, brown ground beef, breaking it up with a spoon, about 5 minutes. Drain excess fat if needed.
03 - Add chopped onion to skillet; cook 3–4 minutes until softened. Stir in garlic, cumin, chili powder, smoked paprika, salt, and black pepper; cook 1 minute until fragrant.
04 - Stir in 1/2 cup enchilada sauce to beef mixture, then remove skillet from heat.
05 - Spread 1/2 cup enchilada sauce on bottom of prepared baking dish.
06 - Arrange 5 tortillas over sauce, tearing to fit as necessary.
07 - Spread half of beef mixture over tortillas. Sprinkle with 1 cup cheddar and 1/2 cup Monterey Jack cheese.
08 - Repeat layering with remaining tortillas, beef mixture, 1/2 cup enchilada sauce, and remaining cheese.
09 - Pour remaining 1/2 cup enchilada sauce evenly over top layer; sprinkle with any reserved cheese.
10 - Cover dish with foil and bake 20 minutes. Remove foil and bake uncovered an additional 10–15 minutes until cheese is bubbly and golden.
11 - Let casserole rest 5–10 minutes before slicing.
12 - Top with sour cream, cilantro, diced avocado, and sliced green onions as desired. Serve warm.