Preheat oven to 350 degrees. Coat an 8-inch square baking pan with cooking spray.

In a medium bowl, combine the flour, baking powder, and salt. Mix well and set aside.

In a separate medium bowl, whisk together the melted butter, sugar, and vanilla. Whisk in the eggs, one at a time. Whisk in the flour mixture until just blended.

Transfer half of the batter to a separate bowl (or the bowl used for the flour mixture so you don't have to clean 3 bowls!). Whisk in the cocoa powder until blended. Fold in the chocolate chips.

Fold the pumpkin puree and pumpkin pie spice into the remaining batter.

Spread half of the chocolate batter into the bottom of the prepared pan. Spread half of the pumpkin batter on top. Using a spoon, add dollops of both remaining batters on top (this makes swirling easier). Using a butter knife, swirl through the dollops to create a swirled top. If desired, sprinkle the top with more chocolate chips.

Bake for 40 to 45 minutes, until a wooden pick comes out clean or with little moist bits clinging to it.

Cool the brownies in the pan, on a wire rack before slicing.

Store leftovers in an airtight container in the refrigerator for up to 5 days, or freeze up to 3 months.