PREP: Preheat the oven to 325 degrees F (162 degrees C). Lightly grease and flour an 8.5 x 4.5-inch bread pan or line with parchment paper and set aside. Melt the coconut oil and then set aside to cool back to room temperature. (Measure coconut oil in melted not solid state.)
ZUCCHINI PREP: Wash and dry the zucchini. Grate on the large holes of a grater. Place on 2 sheets of paper towel or a clean kitchen towel and squeeze 1-2 times. We don't want to remove too much liquid, just a bit. Set aside.
WET INGREDIENTS: In a large bowl, combine Greek yogurt, vanilla extract, 1 large egg, coconut oil (melted, but cooled), and honey. In a separate small bowl, thoroughly mash the overripe banana to the consistency of applesauce. Add the mashed banana and brown sugar to the bowl. Briskly whisk ingredients together until smooth and combined.
DRY INGREDIENTS: In a separate medium-sized bowl, stir together the oat flour (See Note 1), white or white-whole wheat flour, baking soda, salt, and cinnamon.
ADD ZUCCHINI: Add the dry to the wet and mix a few times before adding in the grated zucchini. Add chocolate chips or nuts, if desired. Mix until ingredients are just combined. Overmixing will result in dense bread.
BAKE: Use a spatula to scrape every bit of the mixture into the prepared pan and smooth the top with the back of the spatula. If desired, press a few more chocolate chips in the top here. Bake for 40-50 minutes or until a toothpick, when inserted into the center, comes out clean or with a few moist crumbs and the bread has begun to slightly pull away from the sides.
COOL BREAD: Remove from the oven and allow to cool for 15 minutes and then remove from the bread pan onto a cooling rack. Let the bread fully cool before cutting into the bread. (It's a bit crumbly right out of the oven.) Cut with a very sharp serrated knife.
STORAGE: This bread stores 1-2 days at normal room temperature (wrapped tightly/stored in an airtight container). After 3-4 days, this bread is more prone to molding because of the ingredients used and the overall moistness of the bread. Warm the refrigerated (unwrapped) slices in the microwave for 5-10 seconds. Freeze any leftover slices for up to 3 months (individually wrapped and then placed in a zip-top bag). To thaw, set out wrapped slices at room temperature for about an hour.