Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line it with parchment paper.
In a large bowl, whisk together the oat flour, baking soda, baking powder, salt, cinnamon, nutmeg, ginger, and cloves until well combined.
In a separate medium bowl, whisk the pumpkin puree, grated zucchini, brown sugar, eggs, vegetable oil, Greek yogurt, and vanilla extract until smooth and fully combined.
Pour the wet ingredients into the dry ingredients and gently fold together with a spatula until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 55 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Remove the bread from the oven and allow it to cool in the pan for 10 minutes.
Transfer the bread to a wire rack and let it cool completely before slicing.