Preheat oven to 350°F. Lightly grease a 9x13 baking dish with cooking spray. Alternatively, you can use a 10-inch cast iron skillet.
In a cast iron skillet or large skillet, add ground beef and onion and brown and crumble ground beef until no longer pink. Drain, if needed, wipe skillet, and return to skillet. Add taco seasoning and stir well to combine. Set aside.
In a large bowl, add eggs and milk. Whisk to combine, then add salsa, salt and pepper, and ½ cup shredded cheese. Stir to combine.
If using a baking dish, spread meat onto bottom of pan and then pour egg mixture over the top. If using the skillet, pour egg mixture over ground beef.
Bake for 25 minutes, remove from oven and top with remaining 1 cup of shredded cheese, and bake for 5-10 more minutes or until cheese is melted and eggs are set and not jiggly in center. Let sit for 5 minutes before serving and add toppings, if desired.
Notes
Casserole will keep in an airtight container at room temperature for up to three days.
See my tips and tricks for making this Taco Egg Bake above the recipe box.