First off, preheat your oven to 180°C and line an 8x8-inch baking pan with parchment paper.
In a large mixing bowl, beat the butter with the brown sugar, then add the pumpkin purée and vanilla extract. Stir until well combined.
In a separate bowl, whisk together the flour, baking powder and salt and mix. Add it to the main bowl and combine until smooth.
Remove 3/4 of a cup of batter and set aside in a separate bowl. To this separate bowl add the extra pumpkin purée, flour and pumpkin pie spice and combine until smooth.
To the main batter, add the sifted cocoa powder and mix until just combined.
Pour the cocoa batter into the prepared baking pan and spread it evenly.
Layer the pumpkin batter on top and either leave it as is or swirl to your heart's content.
Bake in the preheated oven for 25-30 minutes, or until a toothpick comes out with a few moist crumbs.
Allow the vegan pumpkin brownies to cool in the pan for at least 15 minutes before lifting them out using the parchment paper.
Once completely cool, cut the vegan pumpkin brownies into squares and enjoy!