In a medium sized bowl, mix together the dry ingredients of the cake.
Add the coconut oil and vanilla extract, followed by the eggs, one by one, beating well after each addition.
Peel and dice the apples into small cubes around 1 cm, and mix into the rest of the batter.
Grease a 9 inch pan, and pour the mixture into the pan. I like to use a silicone square pan.
Prepare the crumb topping by mixing all of the dry ingredients together until well combined.
Melt the coconut oil, if it isn't already liquid, and slowly pour the oil into the dry ingredients, mixing all of the while, until large crumbs start to form. At first the mixture will resemble wet sand, but as you add more oil into the mixture, balls of dough will start to form.
Pour the crumb toping over the cake mixture in the pan, pressing down on them until they stick to the top of the cake.
Bake for 35-40 minutes, or until a toothpick inserted into the center of the cake comes out clean.