Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper or greased foil.
In a medium saucepan, melt the butter and chocolate over medium low heat, stirring until smooth.
Remove from heat and stir in the sugar.
Stir in the eggs one at a time, followed by the vanilla extract.
Stir in the flour, salt and cinnamon and mix until just combined. Stir in most of the chopped pecans if using, reserving a few for the top of the brownies.
Spread about half of the chocolate brownie batter into the bottom of the prepared baking pan. This layer will be very thin, barely covering the whole pan.
Dollop spoonfuls of the pumpkin filling on top of the brownie batter, then dollop the remaining brownie batter on top.
Take a knife and run it through the batter, swirling the brownie batter and pumpkin filling together. Sprinkle the top with chocolate chips and reserved chopped pecans.
Bake until for about 35 minutes, or until cheesecake filling is set and brownie batter swirls appear dry.
Let brownies cool completely before slicing. Store in the fridge until ready to serve.
Store brownies in an airtight container in the fridge for up to 1 week and tightly wrapped in the freezer for up to 2 months.