Preheat oven to 350 degrees Fahrenheit. Grease a loaf pan (8x4x2) with coconut oil or cooking spray. Line the loaf pan with parchment paper.
Make your flax eggs in a small bowl and set aside for at least 5 minutes. Grate the zucchini and carrots, squeeze out the excess liquid, and set aside.
In a large bowl, combine coconut sugar, white rice flour, almond flour, arrowroot starch, baking powder, baking soda, salt, cinnamon, and ginger. Whisk to combine. Add flax eggs, coconut oil, lemon juice, maple syrup, and vanilla extract. Stir until mixture is evenly combined.
Fold in zucchini, carrots, and chopped walnuts. Transfer batter to prepared loaf pan. Shake gently side to side to even out batter. Bake for 40-50 minutes. A toothpick should come out almost completely clean and the center should be set. Allow cake to cool completely in pan on a wire rack.
While the cake bakes, allow your cashews to soak in hot water for at least 10 minutes. Drain the cashews and rinse them. Transfer cashews to a high speed blender.
Add maple syrup, almond milk (starting with 1 or 2 tablespoons, add more after blending if needed), lemon juice, vanilla extract, and cinnamon. Blend on high until smooth. Place cashew frosting in the refrigerator until it is time to frost.
Use parchment paper flaps to remove cake from pan. Frost with cashew frosting or other desired frosting and top with additional walnuts. Slice and serve.