Preheat your oven to 375°F (190°C). Heat a skillet over medium heat. Add the ground beef and onion, cooking until the beef is browned and the onion is soft. Drain excess fat if necessary. Stir in the taco seasoning, black beans, diced tomatoes, and corn. Let it simmer for 5 minutes. In a greased baking dish, layer half of the crushed tortilla chips at the bottom. Add the beef mixture, spreading it evenly. Sprinkle 1 cup of cheese over the beef layer. Repeat with another layer of chips, beef mixture, and the remaining cheese. Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, until the cheese is melted and bubbly. Remove from the oven and let the casserole rest for 5 minutes. Garnish with sour cream and fresh cilantro if desired.