Preheat the oven to 350 degrees F. Line an 8×8 square pan with parchment paper and set aside.
Begin by making the cake. In a large bowl, add all the dry ingredients and mix well. Once well combined, add in all the wet ingredients and mix until you have a uniform thick batter. Set aside.
Next, make the filling. In a small bowl, mix together the coconut sugar and the cinnamon.
Spread half the batter into your lined pan. Sprinkle the filling over the top. Add the other half of the batter over the filling and spread evenly.
In a bowl add the flour, coconut sugar, and melted butter. Mix together with a spoon or your fingers until it has formed large crumbs (see photo above).
Top the cake evenly with the crumb topping and bake the cake for 30-35 minutes, or until a toothpick comes out clean. Once a toothpick comes out clean, remove the cake from the oven. Let cool completely at room temperature before cutting and serving.