Preheat the oven to 350ºF. Line the bottom of a 9-inch cake pan with a circle of parchment paper. Grease the paper and the sides of the pan with coconut oil.
In a large bowl, whisk together the almond flour, cinnamon, baking powder, and salt. In a separate bowl, combine the applesauce, sugar, eggs, and orange zest.
In a small pot over low heat, melt together the honey and coconut oil. Pour into the egg mixture and whisk until smooth. Add the liquid ingredients to the flour mixture and mix to combine thoroughly. Stir in the diced apple. Pour the batter into the greased pan and spread out evenly. Sprinkle the slivered almonds on top.
Bake for 40-50 minutes or until golden brown and a toothpick inserted into the center of the cake comes out clean. Cool in the pan for 30 minutes, then run a knife around the edge of the cake to loosen. Carefully invert the cake onto a plate, then invert from the plate to a wire rack to finish cooling.
Cut into slices and serve with ice cream, if desired. Can be made up to 1 day in advance. Wrap in plastic wrap and store in the refrigerator.