Preheat your oven to 350°F (175°C).
In a large skillet, brown the ground beef over medium heat until fully cooked. Drain any excess fat.
Add the taco seasoning mix to the beef according to the package instructions. Mix well and let simmer for about 5 minutes.
In a mixing bowl, combine the sour cream and cream of mushroom soup until smooth.
In the baking dish, spread half of the Doritos evenly across the bottom.
Layer half of the meat mixture over the Doritos, followed by half of the sour cream mixture, and then half of the shredded cheddar cheese.
Repeat the layers with the remaining Doritos, meat mixture, sour cream mixture, and finish with the last half of the cheddar cheese.
If desired, sprinkle black beans and diced green chilies on top for extra flavor.
Cover the baking dish with aluminum foil and bake for 20 minutes.
After 20 minutes, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbling and golden.
Allow the casserole to cool for a few minutes before serving. Garnish with chopped green onions.