Cheesy Taco Casserole

Preheat oven to 375°. In a large skillet over medium heat, heat oil. Add onion and cook until soft, about 5 minutes. Stir in garlic and cook until fragrant, about 1 minute more. Add ground beef, breaking up the meat with a wooden spoon. Cook until beef is no longer pink, about 6 minutes. Drain fat.  Stir in taco seasoning, then season to taste with salt and pepper. Stir in everything but ¼ cup black beans, 1 1/2 cups cherry tomatoes, and corn.  Spread a small amount of the beef mixture on the bottom of your baking dish, then top with a layer of tortillas. Add a third of the cheeses, 1/3 of the meat mixture, then repeat with another layer of tortillas, cheese and beef. Top with remaining tortillas and remaining meat mixture. Top with crushed corn chips, remaining cheese, and reserved beans. Bake until cheese is melty and casserole is warmed through, 20 to 25 minutes. Garnish with remaining cherry tomatoes and green onions. Serve with sour cream.