Preheat oven to 350 degrees F. Line an 8″x8″ baking dish with parchment paper.
In a large mixing bowl, mix together almond flour, salt, and baking soda.
In a separate bowl, whisk together applesauce, yogurt, eggs, maple syrup, vanilla, and lemon zest until well combined with no lumps.
Pour wet ingredients into dry, and mix together.
Pour cake batter into the prepared baking dish.
Layer apple slices evenly over the cake batter.
Use a fork to mash together all the streusel topping ingredients in a bowl. Mixture should be crumbly.
Use your hands to sprinkle the streusel topping evenly over the apple slices.
Bake for 45 minutes – 1 hour, until cake is not jiggy when moved, and a toothpick comes out clean in the center. Edges will be nicely browned to a deep caramel color.
Let cool completely before slicing into 16 squares.
