In a bowl, stir together the flour, baking powder, and salt.
In a separate bowl, stir together the melted butter, sugar, and vanilla. Using a spoon, mix in eggs one at a time. Gradually stir in your flour mixture, and divide the batter evenly among two separate bowls.
Stir cocoa powder and chocolate chips into one batter. In the second bowl of batter, stir in the pumpkin puree, walnuts, cinnamon, cloves, and nutmeg.
Spread ½ of the chocolate batter into the bottom of a greased 8x8 baking pan. Spread ½ of the pumpkin batter on top of that.
Add dollops of each of the remaining batters into the baking pan (this will make it easier to swirl). Then, drag a kitchen knife gently through the dollops of chocolate and pumpkin batter to create a swirled top.