Preheat your oven to 350 degrees F. Line a baking sheet with parchment paper and set aside. (Using a silicone baking mat will cause the cookies will spread more than parchment.)
In a medium mixing bowl whisk together the flour, cinnamon, baking soda, and salt until well combined.
In a large mixing bowl, beat together the butter, brown sugar, and sugar until smooth and fluffy, about 1 minute. (You can also do this in a stand mixer with the paddle attachment.) Add the eggs and vanilla to the bowl and mix.
Add the dry ingredients in two additions mixing until just combined after each addition. Scrape the sides of the bowl as needed. Add the oats to the bowl and mix everything together.
Using a small cookie scoop (about 1 1/2 tablespoons) to portion the cookie dough. Then use your hands to roll the scoops into round dough balls before placing them on the cookie sheet. The dough will be sticky so you may want to lightly flour your hands.
Bake the cookies for 11 minutes. Remove them from the oven and allow the cookies to cool on the baking sheet for about 1 minute before transferring to a wire rack to cool completely.