Preheat your oven to 180 degrees celsius (360 Fahrenheit) , and line a cake tin. I use a 21 cm square cake tin.
Place all the crumble topping ingredients in your food processor, pulse until a crumble topping forms. Set the topping aside.
Sift the flour, cocoa,mixed spice and baking soda (being sure to crush any large lumps of baking soda) into a large mixing bowl.
Add the second measure of brown sugar and use a whisk or fork to combine it with the other dry ingredients.
Grate the apples, and add to dry ingredients along with the oil and eggs.
Combine with a wooden spoon.
Spoon the cake batter into your prepared cake tin, and sprinkle on the crumble topping.
Bake for 25-30 minutes until the centre of the cake springs back when pressed.