Step 1: Preheat the Oven : Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with oil or nonstick spray.
Step 2: Cook the Ground Beef : Heat a large skillet over medium-high heat. Add olive oil, then the ground beef. Cook until browned, breaking it apart with a spatula (about 5–7 minutes). Drain excess grease.
Step 3: Add Flavor : Add chopped onion and minced garlic to the beef. Cook 2–3 minutes until fragrant and softened. Stir in taco seasoning and water. Mix well and simmer until most of the liquid evaporates.
Step 4: Add Beans, Corn, and Tomatoes : Stir in the black beans, corn, and diced tomatoes with chilies. Cook for 3–4 minutes, allowing the flavors to meld. Remove from heat.
Step 5: Assemble the Casserole : Spread half of the crushed tortilla chips on the bottom of the baking dish. Layer the beef mixture evenly over the chips. Spoon sour cream on top and spread it gently. Sprinkle with 1 cup of shredded cheese. Add the remaining tortilla chips on top. Finish with the remaining cheese.
Step 6: Bake : Bake uncovered for 20–25 minutes, or until cheese is melted and bubbly. If you like extra crispy chips on top, broil for the last 2–3 minutes.
Step 7: Garnish and Serve : Let the casserole rest for 5–10 minutes before serving (this helps it set). Top with your favorite taco fixings — diced tomatoes, lettuce, avocado, salsa, and a dollop of sour cream.