Preheat the oven to 350F and line a baking sheet with parchment paper.
Make the dough:
In a medium bowl, combine the oats, flour, baking soda, salt, cinnamon, and pumpkin pie spice.
In another bowl, pour the melted butter. Add the sugars and whisk to combine. Add the egg and vanilla extract and whisk into the sugary mixture. Once cohesive, add the pumpkin puree and whisk until smooth.
Slowly add the oat mixture to the wet ingredients and continue folding the mixture until a thick dough is formed. Fold in the pecans if using.
Form the cookies:
Scoop about 2 tablespoon-sized balls of cookie dough onto the parchment-lined baking sheet.
Using your hands, flatten them down into round cookies (they don't spread).
Bake:
Bake for 14 to 15 minutes until the tops are light brown and the middle of the cookies are not wet.
Remove from oven and allow cookies to cool down for 10 minutes.