Preparation:
Preheat the oven to 350°F (175°C). Grease a 9x13-inch baking dish to ensure the casserole does not stick.
Cook the Beef:
In a large skillet over medium heat, add the lean ground beef. Use a spatula to break apart the meat as it cooks. Continue cooking until the beef is browned throughout. Once browned, drain any excess grease from the skillet.
Sauté the Vegetables:
Return the skillet to the stove. Add the finely diced yellow onion and red bell pepper. Sauté the vegetables for 3 to 4 minutes until the onion becomes translucent and the pepper is tender.
Season and Simmer:
Sprinkle the taco seasoning over the beef and vegetables. Add the water or beef broth to the skillet. Reduce the heat to low and let the mixture simmer for 5 to 6 minutes, allowing the flavors to meld and the liquid to reduce slightly.
Combine Ingredients:
Stir in the drained tomatoes with green chilies, drained and rinsed black beans, and sour cream. Mix until all ingredients are thoroughly combined. Remove the skillet from the heat.
Assemble the Casserole:
Slightly crush about 1 cup of Cool Ranch Doritos and spread them evenly on the bottom of the prepared baking dish. Spoon half of the beef mixture over the crushed Doritos, spreading it in an even layer. Sprinkle half of the shredded Mexican blend cheese over the beef mixture. Add another layer of crushed Doritos, followed by the remaining beef mixture. Top with the final layer of Doritos and the remaining cheese.
Bake:
Place the baking dish in the preheated oven. Bake for 25 to 30 minutes, or until the casserole is bubbling and the cheese is golden brown and slightly crispy.
Serve:
Remove the casserole from the oven. Let it sit for a few minutes before serving. Serve hot, topped with additional sour cream, salsa, and a sprinkle of sliced green onions. Enjoy the rich, layered flavors of the "Cheesy Beef Nacho Bake."