Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine pumpkin puree, granulated sugar, brown sugar, and vegetable oil.
Add the eggs and vanilla extract to the mixture, and whisk until smooth.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, baking soda, cinnamon, nutmeg, and salt.
Gradually fold the dry ingredients into the wet mixture until just combined.
If using, gently fold in the chocolate chips.
Line a muffin tin with paper liners and fill each cup about two-thirds full with batter.
Bake in the preheated oven for 18-20 minutes, or until a toothpick comes out clean.
Allow the muffins to cool in the pan for 5 minutes, then transfer to a wire rack.
Enjoy your scrumptious chocolate pumpkin muffins warm or at room temperature.