Heat oven to 200°C/400°F. Put all filling ingredients in an ovenproof dish, toss to coat with the olive oil, and roast for 15 minutes. Meanwhile, make the topping.
Put all the topping ingredients in a bowl and mix.
Remove the filling from the oven and sprinkle the topping evenly over it.
Reduce the heat to 180°C/350°F. Put the dish back in the oven and bake until the crumble is golden brown, for about 20 minutes.