Line a baking sheet with parchment paper, then set aside.
In a large mixing bowl, beat the softened butter, white sugar, and brown sugar until well combined and a little fluffy.
Add the egg and vanilla to the butter mixture, then mix until smooth.
Blot the pumpkin puree well with a paper towel to remove excess moisture. Add the pumpkin puree to the sugar mixture and mix until fully combined.
In a medium bowl add the flour, rolled oats, baking soda, cinnamon, nutmeg, and salt. Mix the dry ingredients together well until combined.
Stir the dry flour and rolled oats mixture into the wet pumpkin batter a little at a time, mixing in between.
Fold in the semi-sweet chocolate chips into the cookie dough and mix well if using.
Place the bowl of cookie dough in the refrigerator. Chill the dough for 30 minutes.
When the dough has about 10 minutes left, preheat the oven to 350 degrees Fahrenheit.
Drop batter with a medium 1 1/2 tablespoons cookie scoop onto the prepared cookie sheet, leaving about 2 inches between cookies.
Bake the cookies for 18-21 minutes until soft and chewy. The middle will still be a little soft, but not wet and the edges will be set.
Then cool cookies on a wire rack and enjoy!