Firstly heat your oven to 180 degrees. Now in a fry pan cook your mushrooms with the tsp of butter and the Italian seasoning until well cooked. Now on a fresh chopping board as your are handling raw chicken we are going to assemble the chicken. Open it out so it is butterflied, and you have the two sides joined together season it with salt and pepper. Next add the cooked mushrooms, then add the mozzarella cheese and spinach. Now close it and use toothpicks to close it so it wont leak while cooking, you can wind these through the edges or a skewer if you have one.