Preheat oven to 350 degrees. Butter 9 in square baking dish and line with parchment paper.
Melt chopped dark chocolate and butter in a heatproof bowl set over a pan of simmering water, stirring occasionally until smooth.
Whisk together flour, baking powder, and salt in a large bowl.
In separate bowl combine sugar, eggs, and vanilla and beat with hand mixer or in stand mixer until fluffy.
Combine egg mixture with flour mixture.
Divide batter between your two bowls. In one bowl add melted chocolate mixture and stir to combine. In the other bowl add Pumpkin, oil, cinnamon, and nutmeg and stir to combine.
Pour half of the chocolate batter into prepared pan and smooth, top with half of pumpkin batter and smooth, the repeat with remaining batter to form another layer of each.
Gently swirl the batter with small knife or spatula to create swirl effect.