Preheat oven to 160ºC.
Add all of the dried ingredients to a mixing bowl and stir well until fully combined.
Make a well in the centre then add the egg, yogurt, maple syrup and olive oil and stir well until it forms into a smooth batter.
Peel the apples, core and dice then fold through the mixture.
Spoon into a lightly oiled muffin tin.
To make the crumble mix together the oats, melted butter, maple syrup and cinnamon, then sprinkle over each muffin.
Bake for 25 minutes until golden brown.
Serve warm or cold.