Grease your slow cooker insert thoroughly with coconut oil or non-stick spray and line with parchment paper.
In a large mixing bowl, combine almond flour, coconut flour, sweetener, cinnamon, nutmeg, ginger, baking powder, baking soda, and salt.
In another bowl, whisk together eggs, melted coconut oil, applesauce, and vanilla extract until smooth.
Fold the grated carrots into the wet ingredients, then add the wet mixture to the dry ingredients, stirring until just combined.
If using, fold in the chopped walnuts gently.
Pour batter into the prepared slow cooker and spread evenly across the bottom.
Place a clean dish towel under the lid and cook on low for 3.5 to 4 hours until the cake is set and a toothpick inserted in the center comes out clean.
Allow the cake to cool completely in the slow cooker before removing and frosting as desired.