Take roughly 5 parts raw spinach to 1 part mushroom (I use porportions because it can vary greatly depending on how many people you are cooking for)
(mushroom should be chopped on their sides and left in flat pieces. it ends up just having a strange texture if you dice them smaller)
sautee in non stick pan with freshly diced garlic and red wine viniger. (merlot viniger seems to work the best in my opinion, very little does the trick. dont over use as your not making soup and you want most of it evaporated within 6 to 8 minutes.)
I am sorry I can not be more precise, this is one of those eye ball it things for the most part. The spinach will seem like way to much but it will shrink like a dehydrated watermellon.