Toss together the ingredients for the filling in a large bowl, then turn friot into the prepared dish.
Heat the pecans in a small dry skillet over medium heat, shaking the pan or stirring the nuts, until they begin to smell toasty.
Remove from the skillet at once and chop the nuts coarsely.
Mix together the oats, flour, sugar, salt and nutmeg in a large bowl or in the bowl of a food processor fitted with the steel blade.
Cut the butter into small pieces and work it into the flour mixture, either by taking up the mixture in handfuls and rubbing it briskly between your fingers and thumbs, or by using the pulse action in the food processor.
The topping should have a crumbly consistency.
Stir in the pecans.
Spoon the crumble topping over the fruit in an even layer.
Bake until browned, about 45 minutes.
Serve warm, with cream or yogurt if you wish.
Advance preparation: The topping will hold for a few hours in the refrigerator.
The crumble can be baked a couple of hours ahead and reheated.