Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
Beat butter and sugar until slightly fluffy.
Add pumpkin, egg, vanilla, and water and mix until combined.
Whisk flour, baking powder, pumpkin pie spice, and salt separately.
Gradually add the dry ingredients to the pumpkin mixture and mix just until incorporated.
Chop pecans.
Fold in the chocolate chips and chopped pecans.
Divide dough in half and shape into two rectangles about 3 inches wide and 9–10 inches long on the prepared baking sheet.
Bake for 20–25 minutes.
Remove from the oven and cool for 10 minutes.
Using a sharp, non-serrated knife, cut each log into 1–1½-inch slices.
Place the slices cut-side down on the baking sheet.
Bake for another 10–15 minutes, until lightly browned and crisp. Cool completely.
Melt the remaining chocolate and drizzle over the cooled biscotti.
Let the chocolate set and serve.