Step 1: Preheat and prepare
Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish or line it with parchment paper.

Step 2: Cook the meat
In a large skillet over medium heat, cook the ground beef and Italian sausage (if using) until browned and no longer pink. Drain excess fat.

Step 3: Sauté the vegetables
Add diced onion and bell pepper to the skillet and cook for 3–4 minutes until softened. Stir in taco seasoning and mix until well coated. Set aside.

Step 4: Prepare the filling
In a large bowl, whisk together the eggs, sour cream, milk, ketchup, garlic powder, salt, and pepper. Stir in the cooked meat mixture and 1 cup of shredded cheese.

Step 5: Assemble the casserole
Spread half of the crushed Doritos on the bottom of the baking dish. Spoon the meat mixture evenly over the chips. Top with the remaining Doritos and sprinkle with the remaining 1/2 cup of cheese.

Step 6: Bake
Bake uncovered for 25–30 minutes, or until the cheese is melted and bubbly and the casserole is heated through.

Step 7: Garnish and serve
Remove from the oven, garnish with green onions or cilantro if desired, and serve hot.