Start by peeling and dicing the apples into small pieces.
Next, melt one tablespoon of butter and a teaspoon of cinnamon together in a medium-sized saucepan over medium-low heat, stirring to combine.
Once it is smooth, add the diced apple pieces and sprinkle with the cinnamon. Cook, stirring, until soft. 5-7 minutes. Remove from the heat and set the pot aside.
Preheat your oven to 350°. Line a 9x9 baking dish with parchment paper and set it aside.
Then, in a large mixing bowl, whisk together the dry cake ingredients - almond flour, baking powder, baking soda, and salt.
Next, stir in the eggs, maple syrup and vanilla. Stir until smooth and well combined.
Gently fold in the softened apples and the Greek yogurt. Pour into the prepared baking dish and set it aside.
Next, add the topping ingredients into a small mixing bowl and mix until they clump together when pressed between your fingers. Sprinkle it evenly over the top of the cake batter in the baking dish.
Place the dish in the oven and bake for 35-45 minutes. Use a toothpick in the center to see if it comes out clean to know if it is cooked through. If the top starts to brown too quickly, cover it with foil while the cake finishes baking.
Once the toothpick test comes out clean, remove the cake from the oven and allow it to cool in the pan for 15-20 minutes.
Use the sides of the parchment paper and carefully lift the cake out of the pan. Transfer it to a wire rack to cool completely - 30 -45 minutes.
Slice into 16 pieces.