Fry bacon in a large pan. When brown remove to paper towels. reduce heat. Peel onion and then half, thinly slice the half and sweat/saute in the bacon fat until translucent. Remove to plate. Place spinach in the pan with the remaining bacon fat and stir constantly until wilted.
Fill pie pan with bacon, onion, spinach and cheese. Mix eggs with milk and add pepper to taste. Pour mixture into pie plate.
Bake at 350 for 45 minutes or until center is solid and a pick comes out clean.