Preheat the oven to Gas 5, 190°C, fan 170°C. Mix all the filling ingredients together.
Cut a sheet of nonstick baking paper about 30x40cm (12x16in) and place on the work surface. Take 2-3 sheets of filo, brushing each with melted butter and overlapping slightly to cover the paper. Layer the pastry sheets, brushing in between with butter until the pastry is used up.
Sprinkle the dry breadcrumbs over the top two-thirds of the filo pastry, leaving a 4cm (1½in) border. Dollop apple filling over the pastry and smooth down lightly.
Flip the 4cm (1½in) of bare edge over the filling. Starting at the top, roll the pastry round, using the paper to lift it. Fold over the ends to seal.
Place on a greased baking tray. Brush with leftover butter.
Bake for 30-40 minutes, until lightly browned. Poke a skewer into centre of strudel to see if the apple is tender. Loosen with a knife, then slide onto a serving dish, dusting with icing sugar.