Preheat oven to 180 degrees celsius (fan-forced).
Grease and line a 23cm spring-form cake tin with baking paper and set aside.
Cream the caster sugar and softened butter with beaters or a stand-mixer until pale and fluffy.
Add the eggs one at a time and beat until well combined.
Add the vanilla extract and beat until combined.
Sift in the self-raising flour and mix on low speed until just combined (do not over-beat).
Pour the cake batter into the prepared tin and spread with a spoon (the mixture will be quite thick and sticky).
Sprinkle over the frozen berries and add an even layer of the tinned apple. Set aside.
In a bowl, use your fingers to rub the plain flour, rolled oats, butter and sugar together until they resemble crumbs. Sprinkle the crumbs over the cake.
Cook in the oven for 60 minutes or until a skewer inserted into the middle comes out clean (it may take a bit longer than 60 minutes depending on your oven).
Allow to cool in the tin for 30 minutes before transferring to a wire rack to cool completely. Serve warm or cold.