Preheat the oven to 350°F
Using a large piece of parchment, cover the bottom and sides of a 10 inch round cake pan. Make sure the parchment is hanging off the sides.
In a blender combine yogurt, sugar, oil, eggs and vanilla mix until well blended.
In a large bowl, add flour, baking powder, salt, cinnamon and apples. Mix together well.
Pour the wet ingredients over the dry one and mix with a spatula.
Spread mixture in the prepared cake pan.
Spread crumb topping evenly, pressing it lightly into the batter.
Bake for 40-50 minutes.
Allow to cool down in the pan for 15 minutes before attempting to remove.
Place on a wire rack and let it cool completely for 30 minutes more.