Preheat your oven to 350 degrees. Line a baking sheet with parchment paper or a silicone baking mat. Set aside.
Combine the eggs, pumpkin puree, sugar, baking powder, & salt in a large bowl. Beat on medium speed until the the mixture is light in color, about 3-4 minutes. Add in the melted baking chocolate & beat an additional 30 seconds until well combined.
Fold in the chopped walnuts & dark chocolate chunks or chips.
In a medium bowl, whisk together the cocoa powder, flour, & pumpkin pie spice.
On low speed, gradually beat the flour/cocoa mixture into the wet mixture until incorporated.
Transfer the dough to your lined baking sheet and form into a flat loaf, about 15 inches long & 5-6 inches wide. Bake for 25 minutes, and then remove from the oven. Turn the heat down to 325.
Allow the loaf to cool for about 5-10 minutes. I like to lightly pat down the loaf with water after it has cooled for about 5 minutes to prevent the loaf from cracking.
Once the loaf has cooled a bit but is still warm, cut into about 1 inch thick slices using a chef's knife.
You can cut your slices on a diagonal, if you wish. I usually just cut them straight across, and then in half.
Once cut, transfer all the slices flat side down back to the baking sheet. Bake an additional 20-25 minutes.
Transfer the baked slices to a wire rack and allow them to cool completely.