Spray a 20cm loose-based cake tin with a little oil. Line it with the filo sheets, leaving any excess pastry hanging over the edge and spraying each sheet with oil. Spoon the cheese and spinach mixture into the tin. Fold the overhanging the pastry up and over the top of the pie (you can freeze the pie at this point if you like, cook it from frozen and make sure the centre is piping hot). Spray the top generously with oil. Bake for 25-30 minutes until or until the pastry is golden brown and crisp. Serve warm or cold.