Preheat your oven to 350ºF. Spray a 9-inch baking pan with cooking spray and set aside.
In a microwave-safe bowl melt butter and chocolate until melted and smooth, about 30 seconds to 1 minute. Set aside.
In a large bowl whisk together flour, baking powder, and salt. Set aside.
In a large bowl whisk together sugar, eggs, and vanilla until light and fluffy, about 5 minutes. Whisk flour mixture in until smooth. Divide the mixture evenly into two bowls.
In one bowl of the mixture add chocolate and stir until smooth.
In the other bowl add the pumpkin, vegetable oil, ground cinnamon, ground nutmeg, and ground ginger.
Pour 1/4 of chocolate mixture into the square pan and spread thinly. Pour the pumpkin mixture on top then the rest of the brownie mixture. Swirl with a knife to add a decorative touch. Bake until set, about 40 minutes. Cool completely and cut into squares.