Preheat the oven to 350°F (175°C).

Heat a large skillet over medium. Add the ground beef and cook, stirring, until browned and no pink remains. Drain excess fat.

Return the skillet to low heat. Stir in the taco seasoning and the refried beans until the mixture is well combined and thick. Taste and adjust seasoning.

Spread half the bag of Doritos in an even layer across the bottom of a 9x13-inch baking dish. Gently crush any very large chips so the layer is even.

Spoon the beef-and-bean mixture over the Doritos and spread it into a uniform layer.

Dollop the salsa over the beef, then sprinkle half of the shredded cheese evenly on top.

Add the remaining Doritos in a single layer, then top with the remaining cheese. Scatter the optional chopped green chilies over the cheese if using.

Bake in the preheated oven for 20–30 minutes, or until the cheese bubbles and the casserole is heated through. If you like a slightly browned top, broil on low for 1–2 minutes watching closely.

Remove from oven. Let rest 5 minutes, then serve warm with spoonfuls of sour cream and a garnish of chopped lettuce and tomatoes.