Preheat oven to 350 degrees F. Line a 9x9 baking pan with foil or parchment paper. Spray bottom of lined pan with non-stick oil.
In a heavy pot on low heat, melt butter and chocolate, stirring until smooth and melted. Remove from heat and set aside.
With an electric mixer, combine sugar and eggs and beat until very well combined. Add in flour, baking powder and salt and stir until combined, but to not overmix.
Divide egg, sugar and flour mixture evenly into two bowls. To one bowl add melted chocolate mixture and stir until combined. In the other bowl, add pumpkin, oil and spices to the mixture and stir until combined.
Layer pumpkin and brownie batters into the 9x9 pan, and use a knife to swirl the batters together. If adding chocolate chips to the top, sprinkle on top of the batter. Bake for approximately 40-45 minutes or until a toothpick inserted into the center comes out almost clean. Allow to cool on a wire rack prior to serving.