Preheat oven to 350 F. Spray a 9 inch pie pan with non-stick spray.
In a large mixing bowl, combine the eggs, egg whites and milk.
Beat on low with an electric mixer for 20 seconds, or until eggs are combined (whichever is first). Set aside.
In a large skillet over medium heat, combine the chopped garlic, diced onion, and chopped mushrooms.
Tear spinach into small pieces and add to skillet. Stir frequently and cook for about 5-7 min or until spinach leaves are wilted and the mushrooms and onions are tender.
Begin to assemble quiche. Layer the spinach and mushroom mixture evenly in the bottom of the pie pan.
Sprinkle the cheddar cheese and ¼ cup of the Parmesan cheese over the top of the spinach mixture. (Reserve ¼ cup of Parmesan cheese for later).
Pour the egg mixture over the top.
Bake in the preheated oven for 35 minutes, or until toothpick is inserted and is clean when removed.
Top with ¼ cup of Parmesean cheese. Let quiche sit for 15 minutes before serving. Serve warm.