In a large bowl, whisk flour, pumpkin pie spice, baking soda, and salt. In another large bowl, using an electric mixer on medium speed, beat butter and brown sugar until light and fluffy, about 2 minutes. Add egg, pumpkin, and maple syrup and beat on medium speed until combined, then gradually add flour mixture and beat until fully combined. Stir in oats and pecans. Cover and refrigerate until cold, about 30 minutes.