Preheat your oven to 180°C (350°F) and line a baking dish with parchment paper.
Cook the sweet potato until soft, then mash it in a large mixing bowl.
Add the buckwheat flour, coconut sugar, gingerbread spice mix, baking powder, and cacao powder (or carob) to the sweet potato. Stir until everything is well-combined into a smooth batter.
Spread the batter evenly in the baking dish and bake for about 20–25 minutes or until a toothpick inserted in the center comes out clean.
Allow the gingerbread to cool completely, then cut it into small cubes for layering.