Preheat the oven to 350 degrees F.
In a medium bowl, beat the egg substitute and milk until well combined. Add the Cheddar cheese, Swiss cheese, spinach, onion powder, nutmeg, salt, and pepper; mix well then pour into the pie crust, if desired, or a pie plate coated with cooking spray.
Bake for 40 to 45 minutes, or until firm. Let sit for 5 minutes.
Slice quiche and serve.