Heat the oven to 350°F and line a 9x9 baking dish with parchment paper.
Melt butter or ghee in a large skillet over medium-low low. Add the thinly sliced apples and stir to coat them with the melted butter.
Then sprinkle the apples with the cinnamon and coconut sugar and stir again.
Cook the apples on medium-low heat, stirring occasionally, until softened. About 5-7 minutes. Set the pan aside.
Meanwhile, in a small mixing bowl, use a fork to mix the crumble ingredients: coconut sugar, almond flour, cinnamon, and melted butter or ghee. Mix it until it forms clumps when pressed. Set this bowl aside.
Next, in a large mixing bowl, whisk together the dry ingredients: almond flour, baking powder and soda, and a pinch of salt.
Then, add the eggs, maple syrup, and vanilla into the dry almond flour mixture and stir until smooth. Do not overmix.
Next, fold in the Greek yogurt. Again, do not overmix.
Then, pour half of the cake batter ingredients into the prepared baking dish. 
Sprinkle half of the crumble layer mixture evenly over the top. Then layer half of the cooked apples on top of the crumble.
Pour in the rest of the batter, followed by the rest of the crumble, and then lay the last of the apples evenly across the top.
Finally, pop the dish in the oven and bake until golden and a toothpick comes out clean, about 35-45 minutes.
Once the cake has baked, remove it from the oven and allow it to cool in the pan for five minutes. Then, carefully transfer the cake to a wire rack.
Once it has cooled completely, about 30 minutes or so, cut it into pieces.