Preheat the oven to 300 degrees and line a baking sheet with parchment paper.
Combine melted butter, sugar, and brown sugar together in a medium-sized mixing bowl with a fork.
Add pumpkin, egg yolk, and vanilla and mix until combined.
Stir in flour, baking soda, salt, cinnamon, and pumpkin pie spice.
Fold in rolled oats and 1/2 cup pecans.
Using a 2 tablespoon cookie scoop, create cookie dough balls and place them 2” apart on the prepared baking sheet.
Press the cookies down slightly, top with extra pecans, and bake for 18-20 minutes.
Remove from the oven when the center looks set and before the edges start to brown.
Let cool on the baking sheet for 5 minutes before transferring to a cooling rack.
While the cookies cool, make the glaze by combining powdered sugar and water and stir until smooth.
Drizzle glaze over cookies, let cool and enjoy.