Step 1: Preheat your oven to 350°F (175°C).
Step 2: In a large skillet, brown the ground beef over medium-high heat. Drain off any excess grease.
Step 3: Add the chopped onion to the skillet with the beef and cook until softened, about 3-5 minutes.
Step 4: Stir in the Ro-tel tomatoes, taco seasoning mix, cream of chicken soup, and 1/2 cup water. Bring to a simmer, then reduce heat and let it cook for 5 minutes, stirring occasionally.
Step 5: Stir in the Ranch Style beans (undrained).
Step 6: Lightly grease a 9x13 inch baking dish. Spread about half of the crushed tortilla chips evenly over the bottom of the dish.
Step 7: Spoon half of the ground beef mixture over the chips. Sprinkle with 1 cup of the shredded cheddar cheese.
Step 8: Repeat the layers: add the remaining half of the crushed tortilla chips, then the remaining ground beef mixture, and finally top with the remaining 1 cup of shredded cheddar cheese.
Step 9: Bake for 20-25 minutes, or until the casserole is bubbly and the cheese is melted and lightly golden.
Step 10: Remove from the oven and let stand for 5 minutes before serving. Serve hot with sour cream and salsa on the side.