wash. pull out stems. and place on whatever you want to bake on.
sorry about the ugly leaves. well it's getting chopped up, so worry not. chop up an onion, the mushroom stems and spinach.
fry chopped onions and stems in a little bit of butter or oil. sprinkle a bit of salt
dip spinach leaves into hot water for about a minute ( sorry no picture :/) . chop up leaves and cut up/grate cheese into the stir fried onion+mushroom stems
stuff , stuff, stuff, as much as you can. into preheated oven 200 C /390 F for 30 minutes or until browned on top.
Go wild - drool, take one ,open mouth wide, and chomp!