Preheat the oven to 375 degrees F (190 degrees C). Grease a 9x13 inch pan. Stir together the flour, baking powder, baking soda, salt and cinnamon; set aside.
In a large bowl, cream together the butter and sugar until smooth. Mix in the pumpkin then beat in the eggs one at a time. Stir in vanilla. Gradually blend in the dry ingredients. Fold in chocolate chips and nuts. Spread the mixture evenly into the prepared pan.
Bake for 35 to 45 minutes in the preheated oven, until a toothpick inserted into the center comes out clean. Cut into bars and serve warm or cooled.