Preheat oven to 350 degrees and lightly grease baking sheets. In a medium mixing bowl stir together flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl with an electric mixer on medium speed cream butter and sugar until fluffy. Beat in pumpkin and egg. On low speed gradually add the flour mixture and mix just until blended. Stir in chocolate chips and walnuts.
Drop dough by rounded tablespoonfuls 2 inches apart on prepared baking sheets. Bake for 10 to 12 minutes. Transfer cookies to cooling racks to cool.