Grease a standard-size loaf pan and line it with a parchment paper sling.
Whisk the oat flour, almond flour, brown sugar, granulated sugar, baking powder, baking soda, salt, cinnamon, and nutmeg in a large bowl until thoroughly combined.
In another bowl, whisk the oil, eggs, and yogurt together until combined. Pour the wet ingredients into the dry ingredients and fold together. Fold in the zucchini and the walnuts if using.
Spread the batter evenly into the prepared pan. Preheat the oven to 350℉ and let the batter rest while the oven heats. Then bake the loaf for 50-55 minutes, until a toothpick inserted comes out clean or with a few moist crumbs clinging to it.
Remove the bread from the oven and cool it in the pan for 1 hour, then turn it out onto a rack to cool completely before slicing for the most sturdy crumb.
Notes
Tips
Dairy free - Swap the Greek yogurt for a non-dairy yogurt or milk of choice.
Refined sugar free - Use maple syrup or coconut sugar for the brown sugar.
Nut free - If you don't do almonds, try tiger nut flour (this is a nut-free flour despite its name) or swap teff flour, and omit the walnuts.
Use a 1:1 flour substitute - You can try your favorite 1:1 all-purpose baking flour in place of the oat flour and almond flour. Use 2 cups of flour blend.
Check the loaf as it bakes - Quick breads can be finicky, and sometimes, depending on your oven temperature, you may need to bake them a bit longer. This gluten free zucchini bread takes less than an hour to bake in my home oven, but you may find it needs more time in yours. Check the bread after 50 minutes, and keep checking in 5-minute intervals to make sure it doesn't overbake.
Squeeze the zucchini - but gently - Some recipes have you squeeze out the water from the shredded zucchini, and some call for you to leave it alone. My method falls somewhere in between. I like to gently squeeze out a bit of the water from the zucchini so that it doesn't make the finished loaf overly wet, but you don't have to completely dry the zucchini either.
Rest the batter - As I always recommend with gluten free batters, let the loaf batter rest in the pan for at least 20 minutes or while the oven preheats. This helps the gluten free flours to hydrate, resulting in a better finished bake.
Double it - Go ahead and double this recipe if you have a lot of zucchini. You can enjoy a freshly baked loaf now and freeze one for later, or share it with friends.