Preheat the oven to 350°F (175°C) and prepare a muffin tin with liners.
In a large bowl, whisk together the pumpkin puree, granulated sugar, brown sugar, and vegetable oil until smooth.
Add the eggs and vanilla extract to the mixture, whisking until fully incorporated.
In another bowl, sift together the flour, cocoa powder, baking soda, baking powder, cinnamon, and salt.
Gradually add the dry ingredients to the wet mixture, stirring until just combined, then fold in the chocolate chips if using.
Scoop the batter into the prepared muffin tin, filling each liner about three-quarters full.
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for about 5 minutes before transferring them to a wire rack.