Preheat oven to 350 degrees.
Place the baby spinach and 2-3 tablespoons of water in a large microwave safe bowl and microwave for 2-3 minutes. Once it's cooled squeeze all of the access water out of the spinach. Set aside.
In another large bowl whisk together egg whites, whole eggs, granulated garlic, and onion powder. Pour into a 9 x 13 baking dish coated with cooking spray.
Place the chicken and spinach in with the eggs. Give it a couple stirs to make sure everything is coated with the eggs.
Bake for 30 minutes or until the eggs are set in the middle.
Cut into 8 squares and place one square on half of a toasted english muffin. Add a slice of cheese, tomato, and 1/4 of an avocado.