Place apple, 2 tablespoons of water, lemon juice and caster sugar in a saucepan. Cover and cook over low-medium heat, stirring occasionally for about 10 minutes until soft, divide the apples between 8 cup size serving dishes.
Mix the berries together and sprinkle over the apples, pushing some of them into the apples.
Place the brown sugar, baking powder, rolled oats and flour in a bowl and mix well.
Use your fingers to rub the butter into the flour mix until it resembles rough breadcrumbs.
Top the apples with the crumble mixture and bake in the oven for 20 minutes or until golden brown and bubbly. Serve warm, with ice-cream, double crème or hot custard.