Preheat the oven to 350 °F. Place oven rack in middle of oven.
Line baking sheets with silicone baking mat or parchment paper.
Using mixer, cream butter with sugars until light and fluffy, around 2 minutes.
Add eggs, one at a time. Then, add vanilla.
Sift or whisk the baking soda, salt, flour and cinnamon together.
Slowly add the dry ingredients to wet mixture, in 3 different additions.
Fold in oats by hand.
Using a medium-sized cookie scoop or table spoon, scoop dough onto cookie sheet.
Bake cookies 10-12 minutes or until lightly browned around the edges.
Remove cookie sheets from oven; allow cookies to cool on sheets 1-2 minutes before moving to wire rack to cool.
Drizzle cookies with icing and allow icing to harden before storing cookies.