Preheat oven to 350 F.

Line a 15x10-inch jelly roll pan with foil; the foil should cover all four sides of the pan. Generously spray foil with oil. Do not use butter as it will burn.

Using a food processor chop onions finely, remove from the bowl, then chop ham; change attachment and grate cheese. In a blender add eggs, milk, flour, salt and melted butter; mix until well combined. Pour egg mixture into pan and sprinkle with onion and ham. Bake until eggs are set, about 10-12 minutes.

Decorate plates with a few spinach leaves. Remove cooked egg from oven and quickly sprinkle with cheese and spinach. Begin at the narrow edge of pan and roll omelet using foil to help lift and roll omelet. Cut rolled omelet into 8 slices and place two slices on each decorated plate.