Preheat oven to 350. Prepare a 9x5 bread loaf pan by either lightly greasing with coconut oil or lining with parchment paper. If using parchment, cut a piece that is as wide as the loaf pan and place parchment on the bottom and up the short sides. This allows you to easily pull on the parchment to remove the bread from the pan when done.
In a large mixing bowl, combine the gluten-free flour, almond flour, coconut flour, cinnamon, nutmeg, baking powder, baking soda, and salt.
In a separate bowl, combine the mashed banana, coconut oil, coconut sugar, eggs, vanilla, and grated zucchini. Whisk together using a metal whisk or a fork. (tip: mix the banana, oil, and sugar together first before adding remaining ingredients; this will help the coconut oil from solidifying when the cold eggs are added).
Add the wet ingredients to the flour mixture and stir until fully combine, but don't overmix. Batter will be on the thicker side.
Scoop batter into prepared loaf pan. Using a knife, spread batter evenly across the top.
Bake for 55-65 minutes, or until a knife inserted in center of bread comes out clean. I usually check the bread at about 35 minutes and tent the pan with a piece of foil (this will help the edges from browning too much).
Let cool 5-10 minutes before removing from pan. Pull on parchment paper to remove. If needed, run a knife along the long sides of the pan to loosen bread.
Allow to fully cool. Slice and enjoy!