Preheat the oven to 350º, and line a 9x13 baking pan with parchment paper. Set aside
Prepare brownie mix according to instructions in a medium or large bowl, THIS IS WHERE YOU USE THE OIL AND EGGS, separate about 1 cup of brownie batter into a smaller bowl, and set both aside
In a mixing bowl, beat butter and sugar together.
Add the other egg, vanilla, pumpkin puree, and spices, and beat until combined.
Whisk in flour
Pour the larger bowl of brownie batter into the prepared baking pan, spread in an even layer across the whole pan to form the bottom brownie layer
spoon the pumpkin mixture on top, and swirl with a butter knife
Drizzle the remaining brownie batter as the top layer, and swirl a bit
Bake in the center of the preheated oven for about 40 minutes, until the edges are set, and the center is still somewhat soft
Let cool completely in the baking dish before removing from the pan and cutting into squares to serve