Preheat the oven to 400°F (200°C) and grease a 9x13-inch baking dish.
Cook the ground beef in a large skillet over medium heat until no longer pink, about 6–8 minutes.
Drain any excess fat, return the skillet to the heat, add the taco seasoning (both 1-ounce packets) and prepare according to package directions, stirring to combine.
Spread the seasoned beef evenly in the prepared 9x13-inch baking dish and set aside.
In a mixing bowl, beat together the eggs and milk until smooth. Stir in 1¼ cups biscuit or baking mix and a dash of black pepper until well combined.
Pour the egg-and-biscuit mixture evenly over the beef in the baking dish.
Bake in the preheated oven until the top is golden brown and set, about 20–25 minutes.
Allow the casserole to cool for a few minutes, then spread 1/2 cup sour cream over the top.
Top with 2 cups chopped lettuce, 3/4–1 cup chopped tomato, 2 cups shredded cheddar cheese, and olives to taste.
Serve the casserole warm.