Grease a 12-inch cast iron skillet* or line with parchment paper.
Add the almond flour, arrowroot, coconut sugar, baking soda, spices, and salt to a large bowl. Whisk to combine.
In a separate large bowl, add the butter, eggs, coconut milk, vanilla, and lemon juice. Mix together using either a stand mixer or a hand held electric mixture.
Add about 1 cup of the dry mixture into the wet mixture at a time, continuing to mix the batter constantly, until all of the dry mixture has been incorporated. Pour the batter into the greased baking dish.
Add all of the crumble ingredients to a bowl and mix to combine. The mixture will be slightly lumpy. Break up and sprinkle the crumble evenly over the top of the cake.
To melt the chocolate either use a double-boiler or microwave it, stirring every 30 seconds, slowly melt the chocolate. Remove the chocolate from heat as soon as all of the solid pieces are gone, then drizzle over the coffee cake.
Bake at 350 F for 35 minutes, until cake is fully set and no longer jiggly in the middle.
Let cool completely, then cut into 10 slices and serve!
*This recipe will also work in a 9×13 inch baking dish or in a bundt pan. The skillet will help create a more crisp crust.