Preheat the oven to 350F (180C). Lightly grease a 9x13 inch (23x33 cm) pan, or line with parchment so that there is an overhang around the edges.
Using a few sheets of paper towel, squeeze out the excess moisture from the pumpkin. Set aside.
In a medium bowl, whisk together the flour, spices, baking soda and salt. Set aside.
In a large bowl, whisk together the melted butter, brown sugar and granulated sugar until no lumps of sugar remain.
Whisk the pumpkin and vanilla into the butter and sugar mixture.
Stir the dry ingredients into the pumpkin mixture until you no longer see lumps or streaks of dry ingredients. I typically do a few stirs with a rubber spatula and then whisk by hand with a wire whisk.
Fold the chocolate chips/chunks into the batter.
Spoon the batter into the prepared pan and smooth into an even layer.
Bake in the preheated oven for 30-40 minutes. Baking closer to 30 minutes will give you a gooier, more blondie-like texture. Baking closer to 40 minutes will make the bars less gooey and a little more cookie-like.
Cool the bars in the pan for at least 30 minutes. For clean cuts, cool until the pan is no longer warm.