Mix almond flour, coconut flour, cinnamon, baking powder, baking soda, salt, and xanthan gum (if using) together, set aside.
In large bowl, combine eggs, oil, sugar, and vanilla until well blended.
Add dry ingredients to wet mixture.
Fold in shredded zucchini and chopped nuts.
Spread batter into prepared pan (I used an 8x4 silicone bread pan).
Place pan in crock pot on a rack or on top of crumpled aluminum foil to raise it at least 1/2 inch from the bottom of the crock. (It's best to raise the pan from the bottom of the crock if you can)
Cover and cook on high for about 3 hours.
Cool completely. Wrap in foil, refrigerate, and enjoy cold. (This bread is best served cold after being in the refrigerator)