Preheat your oven to 350°F (175°C). Line a 9-inch round cake pan with parchment paper or grease thoroughly with coconut oil. For guaranteed easy release, add a light dusting of gluten-free flour after greasing.
Peel and core the apples, then dice them into approximately 1/4-inch cubes. Toss the diced apples with 1 teaspoon of lemon juice to prevent browning if you're working ahead.
In a medium bowl, whisk together the gluten-free flour, cinnamon, nutmeg, cloves, baking powder, baking soda, and salt.
In a large bowl, whisk together the coconut sugar, applesauce, melted coconut oil, eggs, almond milk, and vanilla extract until smooth and well combined.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined. Avoid overmixing. The batter will be slightly thicker than traditional cake batter.
Gently fold in the diced apples, ensuring they're evenly distributed throughout the batter.
If making the crumb topping, in a small bowl, combine the gluten-free flour, coconut sugar, chopped nuts (if using), and cinnamon. Cut in the cold coconut oil using a fork or your fingertips until the mixture resembles coarse crumbs.
Pour the batter into your prepared cake pan, spreading it evenly. If using the crumb topping, sprinkle it evenly over the batter.
Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean with just a few moist crumbs.
Allow the cake to cool in the pan for 20 minutes before transferring to a wire rack to cool completely.