Heat oven to 350. Line sheet pan with parchment paper and grease generously - let parchment hang over the sides of the pan.
Beat together flour, milk, eggs and salt.
Pour into pan and sprinkle with bacon and onions.
Bake 15 minutes until eggs are set.
Immediately sprinkle with cheese, spinach and basil. Roll up from wide side, using parchment paper to lift omelet. Let stand a few minutes and then slice. VEGETARIAN VERSION: Replace meat with mushrooms, peppers, etc...