Roll out the pastry to line a rectangular baking tray or flan tin. Prick the base, line with foil and baking beads, and bake blind at 200 degrees C for 15 minutes. Remove the beads and foil and bake for another 5 mins.
Mix the sausage meat with the onion, lemon, garlic and herbs.
Heat the oil in a pan and fry the sausage mixture for about 5 minutes.
Add the celery, followed by the tomato and pear, mixing well til heated through. Take off the heat.
Spread the mustard onto your baked pie base. Add the sausage mixture, making sure the ingredients are spread evenly.