1. Heat half the olive oil in a large sauté pan and fry the mushrooms for 10 minutes or until they start to brown. Remove from the pan and reserve.
2. Add the rest of the oil to the pan and fry the onion, ginger and garlic for 10 minutes without colouring.
3. Add the chickpeas and vegetable stock and bring to a simmer. Add the chard and cook for 2 minutes to wilt it. Leave to cool for 10 minutes.
4. Preheat the oven to 190°C (170° fan). Brush the base and sides of a 23 cm (9-inch) round springform cake tin with melted butter. Use two-thirds of the filo pastry to line the base and sides of the tin, brushing each layer with butter as you go.
5. Stir the mushrooms and feta cheese into the chickpea mixture and taste it for seasoning, adding salt or black pepper if necessary. Spoon the filling into the pastry case, then fold over the overhanging sides of the pastry. Brush the rest of the filo sheets with butter and cover the top of the pie, scrunching the pastry a little. Any leftover butter can be poured over the top.
6. Bake the pie for 40 minutes or until the pastry is golden brown and the filling is piping hot in the centre.