Preheat oven to 375 degrees F. Line 16 muffin tins with paper liners.
In a small bowl, whisk together flour, baking soda, cinnamon, and cocoa powder. Set aside.
In a large bowl, whisk pumpkin puree and melted butter. Whisk in eggs, brown sugar, and vanilla. Fold in dry ingredients until just combined, then gently fold in chocolate chips.
Fill each of the tins half way. Using a ½ teaspoon, add a dollop of Nutella, then top with batter. Swirl with a knife. Bake for 15-18 minutes, or until a tooth pick inserted in the center comes out clean.
Recipe by The Messy Baker Blog at http://themessybakerblog.com/2012/10/08/muffinmondaynutella-swirl-pumpkin-chocolate-muffins/