Preheat oven to 350°F. Line a 9x5-inch loaf pan with parchment paper, leaving some overhang on the sides for easy removal.
In a large mixing bowl, whisk together the pumpkin purée, eggs, Greek yogurt, avocado oil, maple syrup and vanilla until smooth.
In a separate bowl, whisk together the flour, protein powder, baking soda, baking powder, pumpkin pie spice, cinnamon and salt.
Gently fold the dry ingredients into the wet ingredients until just combined. Do not overmix. The batter should be thick but spreadable. If it seems unusually stiff, add 1–2 tablespoons of milk.
Pour the batter into the prepared loaf pan and smooth the top.
Sprinkle evenly with rolled oats, pumpkin seeds, chia seeds and optional coarse sugar.
Bake for 55–70 minutes, checking around the 50-minute mark. If the top begins to brown too quickly, loosely cover the loaf with aluminum foil.
The bread is done when a toothpick inserted into the center comes out without wet batter.
Allow the bread to cool in the pan for 15 minutes before transferring it to a wire rack. Cool completely before slicing.