1. Preheat the oven to 350 degrees. Line two baking trays with parchment or silicone liners and set aside.
2. Combine the butter and two sugars in a mixing bowl. Beat until light and fluffy, roughly 4 minutes.
3. Stir in the egg and vanilla extract.
4. In a large measuring cup, whisk together the flour, baking soda, salt, and cinnamon. Mix into the butter mixture.
5. Fold in the oats and the chocolate chips.
6. Optional, chill the dough at least 1 hour or up to 8.
7. Scoop the cookie dough into round balls that are 1/4 cup per cookie, and place 3 inches apart on the tray.
8. Bake 10 minutes, or just until the edges are slightly browned. Cool on the tray.