Preheat oven to 350F. Sauté Brussel Sprouts, leek, minced garlic and oil until soft and tender.
Meanwhile, defrost and squeeze dry frozen spinach.
Whisk eggs, egg whites, seasoning and spinach.
Add Brussel sprout mixture and feta to a 9 x13 greased casserole dish.
Pour egg mixture over Brussel Sprout mixture, make sure eggs cover bottom of dish.
Bake 35-45 minutes or until eggs are set. Allow to cool 10 minutes before serving.