Preheat your oven to 375°F (190°C). Line two large baking sheets with parchment paper or silicone baking mats.

In a medium bowl, whisk together the all-purpose flour, baking soda, salt, and ground cinnamon (if using). Set aside.

In a large mixing bowl, using an electric mixer (stand mixer with paddle attachment or a hand mixer), cream together the softened unsalted butter, granulated sugar, and packed light brown sugar on medium speed until the mixture is light and fluffy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Beat in the large eggs one at a time, mixing well after each addition. Stir in the vanilla extract until just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough.

Using a rubber spatula or a sturdy spoon, stir in the old-fashioned rolled oats and semi-sweet chocolate chips until evenly distributed throughout the dough.

Drop rounded tablespoons of cookie dough (or use a 1.5-inch cookie scoop) onto the prepared baking sheets, leaving about 2 inches between each cookie. Do not flatten the dough balls.

Bake for 10-12 minutes, or until the edges are golden brown and the centers are still slightly soft. Baking time may vary slightly depending on your oven.

Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire cooling rack to cool completely.