Preheat oven to 350 degrees. Crack the eggs into a bowl and beat until yolks are mixed in. Place fresh spinach and milk into a food processor or blender. Blend together until smooth. Mix into eggs. Add salt and pepper. Pour into a square glass casserole dish sprayed with cooking spray. Bake for 10 minutes. Use a spatula to scrape and stir just as you would for scrambled eggs on the stovetop. Bake 10 more minutes and repeat with the spatula. Bake about 5 more minutes. Sprinkle with shredded mozzarella cheese when done.