1) Preheat the oven to 190°C/Gas 5. Spray a 20cm square baking dish with cooking spray.
2) Combine the topping ingredients in a medium bowl and work together with a fork or with your fingertips until the ingredients are moistened.
3) For the filling, combine the pear slices, lemon juice and ginger in a large bowl. Add the sugar and flour and toss to blend.
4) Transfer the pear mixture to the dish. Sprinkle the topping over the pears.
5) Bake the crumble until the pears are tender and the topping is golden brown, about 40 mins. Allow to cool for 10 mins before serving. Serve warm or at room temperature, with a scoop of ice cream or frozen yoghurt, if desired.