In a large skillet over medium heat, add the ground beef and diced onion. Cook until the beef is browned and the onions are translucent, about 5-7 minutes. Drain any excess fat.
Stir in the diced green chiles, undrained diced tomatoes, and taco seasoning. Cook for an additional 3-5 minutes, allowing the flavors to meld together.
In your 9x13-inch baking dish, spread an even layer of refried beans at the bottom. This will serve as the creamy base for your casserole.
Spoon the seasoned ground beef mixture over the layer of refried beans, spreading it evenly.
Dollop the sour cream over the meat mixture and gently spread it out, creating a creamy layer.
Sprinkle the crushed tortilla chips evenly over the sour cream layer, adding a delightful crunch to the casserole.
Finally, top the crushed chips with shredded Mexican-style cheese blend, ensuring it covers the entire surface.
Preheat your oven to 350°F (175°C). Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.