Put a baking sheet in the oven and heat to 220C/fan 200C/gas 7. Roll out the pastry and put on a large sheet of parchment paper or cut out 4 individual square tarts. Chill. Peel, seed and cut the squash into ½ cm thick slices. Prick the pastry a few times with a fork and then lay the squash over in a single layer and season. Slide the tart(s) onto the hot baking sheet and cook for 10 minutes. Add the crumbled feta and bake another 10-15 minutes until pastry is crisp and golden.