Preheat oven to 350 degrees F. Line two large baking sheet with parchment paper and set aside.
In a medium bowl, whisk together the oats, flour, baking soda, salt, and cinnamon. Set aside.
With a mixer at medium speed, beat together the butter, peanut butter, and sugars until creamy, for about 2 minutes. Add the egg and vanilla extract. Mix until well combined.
With the mixer on low, add in the dry ingredients and mix until just combined.
Shape cookie dough into round balls and place on the prepared baking sheets, leaving about 2 inches in between cookies. Bake for 10-12 minutes, until the cookies are lightly browned around the edges, but still soft in the middle.
Remove cookies from oven and let cool on the baking sheet for about 5 minutes. Transfer to a wire rack and cool completely.