Preheat your oven to 350°F (175°C). Grease a standard 9x5-inch loaf pan well with cooking spray or a thin layer of butter, then line it with a strip of parchment paper leaving an overhang on the two long sides for easy lifting.

Pull your Greek yogurt and eggs out of the refrigerator 20–30 minutes before starting to bring them to room temperature — this ensures an even, tender bake.

In a large bowl, whisk together the whole-wheat pastry flour, baking soda, baking powder, salt, pumpkin pie spice, cinnamon, and coconut sugar until fully combined and there are no lumps.

In a separate medium bowl, whisk together the pumpkin puree, Greek yogurt, eggs, avocado oil, and vanilla extract until smooth and well combined.

Pour the wet ingredients into the bowl of dry ingredients and fold gently with a spatula until just combined — stop as soon as you no longer see dry streaks of flour. Do not overmix. If using walnuts or chocolate chips, fold them in now with just 2–3 strokes.

The batter will be thick. Transfer it to the prepared loaf pan and spread it into an even layer using the back of your spatula.

Bake at 350°F for 50–60 minutes, tenting loosely with aluminum foil after 30 minutes if the top is browning too quickly.

The bread is done when a toothpick or wooden skewer inserted into the very center comes out with just a few moist crumbs (not wet batter). Begin checking at the 50-minute mark.

Allow the bread to cool in the pan on a wire rack for 15 minutes, then use the parchment paper overhang to lift it out and transfer directly to the rack. Cool for at least 30 more minutes before slicing — cutting too early will cause the crumb to collapse and appear gummy.