Spray a pan with some low calorie cooking spray, sauté the onion and chicken until they start to colour.
Add in the mushrooms and continue to cook until the chicken is almost cooked through (it should take about 10 minutes).
Add the white wine vinegar, Worcestershire sauce and stock. Stir and allow to reduce slightly. Mix the cornflour with a little water, then stir this into the mix until it's thickened.
Remove from the heat and allow to cool for a minute or two.
Pre heat the oven to 180°C.
Stir the quark into the pie mix. Check the seasoning and add some sea salt and freshly ground black pepper if necessary.
Pour the pie filling into an oven proof dish (we used a 19 cm shallow dish but you can use a smaller deeper one if you want).
Take one sheet of filo, lay it out flat and spray generously with low calorie cooking spray.
Cut the sheet into 8 even pieces. Scrunch each piece up lightly then place them on top of the pie filling. Try to leave as fewer gaps as possible.
Spray with a little more low calorie cooking spray.
Place the dish on a baking tray (just in case it drips) and cook for 15-20 minutes or until the filo is golden brown and crisp all over.
Remove from the oven and serve.