Preheat oven to 350 degrees F. Line an 8 ½" x 4 ½" loaf pan with parchment paper and set aside.
In a large bowl, combine ground flax and water. Set aside for 5 minutes to thicken while you gather your remaining ingredients.
To the flax mixture, once thickened, add the coconut sugar and maple syrup. Stir to combine.
Add the shredded zucchini, applesauce, coconut oil, and vanilla, stirring until just combine. Careful not to over mix.
In a small bowl, combine the flours, cinnamon, baking soda, baking powder, and salt. Add this to the wet ingredients and stir until just combined. Fold in the walnuts if using.
Pour batter into prepared pan and place in preheated oven. Bake for 30-37 minutes or until toothpick comes out clean. Allow to cook on a wire rack for 45 minutes before removing from the pan. Cool completely before slicing.