Preheat your oven to 350°F (175°C). Grease a 9×5 inch loaf pan with butter or non-stick cooking spray. You can also line the bottom with parchment paper for easier removal after baking.
In a medium-sized mixing bowl, whisk together the flour, baking soda, baking powder, salt, and pumpkin pie spice. Ensuring these are well-combined helps the bread rise evenly and prevents spice clumps.
In a large bowl, beat the eggs with the granulated sugar and brown sugar until smooth. Add the pumpkin puree, oil, Greek yogurt, and vanilla extract. Whisk until the mixture is creamy and fully incorporated.
Slowly fold the dry ingredients into the wet ingredients using a spatula. Mix just until no streaks of flour remain. Be careful not to overmix, as this can make the bread tough.
Gently fold in half a cup of the chopped walnuts into the batter. Save the remaining walnuts to sprinkle on top of the loaf for an attractive, crunchy finish.
Pour the batter into the prepared loaf pan and smooth the top. Sprinkle the remaining walnuts over the surface. Bake for 55 to 65 minutes, or until a toothpick inserted into the center comes out clean. Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack.