Preheat the oven to 190 degrees C. Grease a 20x30cm pan. Stir together the flour, baking powder, bicarb 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 centre comes out clean. Cut into bars and serve warm or cooled.