Preheat oven to 350 degrees Fahrenheit. Lightly grease a 9x13 pan.
In a large skillet over medium-high heat, cook onion in the butter until the onion softens and starts to brown a bit, about 3-5 minutes. Add in beef, green chiles, cumin, salt, chili and garlic powder and cook beef until it browns, about 6-8 minutes.
In a separate skillet, brown the corn tortilla halves in a very small amount of oil in a pan over medium heat. Flip after about 1 minute and get both sides of tortilla golden in color.
Line the bottom of a 9x13 dish with 8 of the tortilla halves. Sprinkle with 1 cup of cheese. Spoon half of the ground beef mixture on top of the cheese layer.
Layer on all of the black beans, then spoon 1 cup of salsa on top of the beans. Layer 6-8 more browned tortilla halves on top of the salsa.
Layer the remaining ground beef across the tortillas, spoon the corn on top of the ground beef and then top that with the remaining cup of salsa. Top the casserole with the remaining 2 cups of shredded cheddar cheese.
Bake, uncovered, until bubbly and cheese is browning, about 25-30 minutes. Garnish with additional toppings as desired.