Preheat the oven to 350°F (175°C). Lightly grease an 8×8-inch baking pan with ghee, butter, or oil.

In a medium bowl, whisk together the gluten-free flour, cinnamon, ginger, nutmeg, baking soda, baking powder, and salt until evenly combined.

In a separate bowl, mash the banana until smooth. Add the egg, milk, melted or softened coconut oil, maple syrup, and vanilla, and whisk until the mixture is uniform.

Pour the dry ingredients into the wet mixture and stir until just incorporated. Fold in the shredded carrots, then gently mix in the raisins and chopped walnuts if using.

Transfer the batter to the prepared pan and spread it into an even layer. Bake for 28–32 minutes, or until a toothpick inserted into the center comes out clean.

While the bars bake, prepare the Greek yogurt frosting and chill it in the refrigerator so it’s cool and slightly firm when the bars are ready.

Remove the baked bars from the oven and let them cool completely in the pan on a wire rack.

Once the bars are fully cooled, spread the chilled Greek yogurt frosting evenly over the top. Optionally sprinkle a pinch of cinnamon over the frosting.

Place the frosted pan in the refrigerator for about 10 minutes to set, then slice into 9 squares and serve.