Preheat the oven to 350˚F. Line a 7×11 inch pan with parchment paper.
In a medium bowl, beat together the pumpkin, egg, egg whites and oil until smooth.
In a separate bowl, mix together the flour, baking powder, cocoa powder, cinnamon, all-spice, nutmeg, salt and brown sugar. Add the the wet ingredients, and mix until fully incorporated. Fold in the chocolate chips.
Pour the batter into the prepared pan and spread evenly. Bake for 15-20 minutes or until a toothpick inserted comes out clean. Cool completely before cutting.