Preheat the oven to 375°F.
Butter an ovenproof dish.
Place the apples, bananas, sugar and water in a saucepan, cover and cook for about 5 to 6 minutes until the fruit has just softened.
To make the crumble topping, place the plain and whole meal flours in a mixing bowl. Rub in the butter until the mixture resembles breadcrumbs.
Stir in the brown sugar, walnuts and oatmeal. Spoon the fruit into the ovenproof dish. Sprinkle the crumble topping over the fruit.
Bake for about 25 to 30 minutes until golden brown.
Serve warm with cream, custard or your favorite ice cream.
