Preheat Oven: Set it to 350°F (175°C) and grease or line a 9-inch round cake pan.
Mix Dry Ingredients: In a large bowl, whisk together 1 1/2 cups almond flour, 1/2 cup coconut flour, 1/2 cup coconut sugar, 1 tsp baking powder, 1/2 tsp baking soda, 1 tsp cinnamon, and 1/4 tsp salt.
Combine Wet Ingredients: In a medium bowl, mix 1/2 cup applesauce, 1/4 cup melted coconut oil, and 3 large eggs.
Blend Together: Stir the wet ingredients into the dry mix until well combined. Gently fold in 1 large diced apple.
Prepare Streusel: Combine 1/4 cup almond flour, 2 tbsp coconut sugar, 2 tbsp melted coconut oil, and 1/2 tsp cinnamon in a small bowl.
Assemble Cake: Pour the batter into the prepared pan and sprinkle the streusel topping evenly over the top.
Bake: Bake for 35 minutes, or until a toothpick inserted into the center comes out clean.
Cool and Serve: Cool in the pan for 10 minutes before transferring to a wire rack. Slice and enjoy!