Preheat oven to 350 degrees Fahrenheit. Grease an 8×8 pan with a little ghee/butter/oil.
Mix your dry ingredients. Add your flour, cinnamon, ginger, nutmeg, baking soda, baking powder, and salt in a medium bowl and whisk to combine.
Mix your wet ingredients. In a separate medium-large bowl, mash your banana until smooth. If needed, melt your oil. Add your egg, milk, melted oil, maple syrup, and vanilla extract and mix well to combine. Add your dry mixture to your wet mixture and mix well. Stir in carrots, raisins, and walnuts.
Bake. Pour the carrot cake batter into your prepared baking dish and bake for 28-32 minutes until a toothpick comes out clean. Let cool.
While the bars bake, make your frosting. Place in the fridge to let the frosting chill until the carrot cake bars cool.
Frost bars. Once the bars are cooled, add frosting and evenly spread it over the bars. I like to sprinkle a little cinnamon on top. Place in the fridge for 10 minutes to let chill.
Enjoy! Slice into 9 pieces and enjoy!