1. Pre heat the oven to 180 degrees. Place the leeks and stock into a large pan on a medium to high heat, then cover and cook for 5-8 mins until starting to soften. Then add the mushrooms and cook for a further for 3 mins with the lid on. Remove the lid, season & and continue to cook until the juices have evaporated. Once cooked tip the veg onto a plate to cool slightly.
2. For each strudel, lightly brush half of each filo sheet with some olive oil. Fold the un-brushed side over against the oiled side. Brush the edges with a little more oil, then spoon a quarter of the veg in the centre & crumble over quarter of the cheese. Fold over the pastry edges, then pinch together to seal in the filling.
3. Place the strudels on a baking tray, brush with any remaining oil and scatter over the poppy seeds. Bake for 20 mins until crisp and golden brown.