Preheat oven to 350ºF.
In a large mixing bowl, cream butter and sugars together until creamy.
Add egg and vanilla. Beat again until smooth.
Add flour, oats, baking soda, and cinnamon. Beat again.
Add pumpkin and beat until dough is uniform.
Stir in chocolate chips.
Using a cookie dough scoop, scoop balls of dough onto a greased baking sheet about 2 inches apart.
Bake for 10-12 minutes or until edges begin to darken.
Allow cookies to cool completely before adding icing.
To prepare icing, beat powdered sugar and butter together.
Slowly add milk while beating until the desired consistency is reached.
Stir in cinnamon.
Transfer icing to a small ziplock baggie. Cut off a small corner of the bag.
Carefully pipe icing onto cooled cookies.