Preheat oven to 350° F. Line 8 muffin tins with paper liners or spritz with cooking spray.
In a skillet, brown beef with onion over medium heat. Stir in Taco Seasoning and cook an additional 3 minutes.
Divide beef mixture over 12 muffins.
In a bowl, whisk together eggs, salt and pepper. Pour over beef mixture and top with tomato and green onion.
Bake 20-22 minutes or until the egg is fully set.