In a large bowl, beat together the butter, brown sugar and granulated sugar. Once that is combined, beat in the egg and vanilla extract for about 1 minute or so until it lightens in color a tad. Then add in the old fashioned oats until combined.
In a separate medium bowl, gently mix together the dry ingredients - flour, baking soda, salt, and cinnamon.
Slowly add in the dry ingredients into the oat mixture (I did in two portions). Once all combined, fold in the chocolate morsels.
Grab a large baking sheet lined with parchment and scoop out 1 tablespoon sized cookie dough balls. Lay them all out on the baking sheet in 1 layer, and put in the fridge for about 45 minutes.
Preheat your oven to 350℉ and bake the cookies for 12 - 14 minutes. 12 minutes if you like them a little more doughy, and 14 if you like them a little more well-done.
Optional: sprinkle with flaky sea salt when they come out of the oven.
Enjoy!