Spread softened butter on one side of two slices of bread. Turn 1 slice over and spread pesto on the other side. Place two slices of cheese on one slice of bread, arrange fresh spinach on the cheese and top with the other slice, butter side out. Coat sandwich with Parmigiano, gently pressing on it. (optional, use if you want to have a Parmesan encrusted grilled cheese) Place the sandwich in a non-stick pan. Cook over medium-low heat until the outside is light golden brown and the cheese has melted. About 2 minutes per side. Transfer to a plate, cut in half and enjoy.