Lightly spray cake tin (round or square medium size) with spray vegetable oil. Preheat oven to 180 degrees celsius (moderate heat).
Cake: Combine in a bowl all dry ingredients (flour, oats, brown sugar, baking powder and baking soda, nutmeg, cinnamon, salt).
Combine in a small separate bowl yogurt and olive oil, then add to dry ingredients.
Add apple juice and eggs and beat until combined, then fold in the apples.
Spoon mixture into prepared cake tin.
Topping: Mix yogurt and olive oil in a bowl.
Combine oats, flour, sugar and grated apple.
Mix until it is a crumbly texture (If too moist you may add pinches of flour, however the crumble effect will still happen after cooked). Crumble mixture over top of cake batter and bake for 30-35 minutes or until cake is firm and bounces back when lightly touched.