Combine the flour, baking soda, cinnamon, and salt in a medium-sized mixing bowl. Mix the dry ingredients using a fork until well combined.

Add the rolled oats and chocolate chips to the flour mixture. Stir with a fork until evenly distributed. Set aside.

In a stand mixer fitted with the paddle attachment, or using a hand mixer, beat the melted butter and sugars on medium speed until the sugar is dissolved, about 3 minutes.

Add the peanut butter to the mixture and beat for an additional minute or until fully incorporated.

Beat in the egg and vanilla extract until well mixed, about 1 minute.

Gradually add the flour mixture to the wet ingredients on low speed, mixing until just combined. Be careful not to overmix, as this can make the cookies tough.

Transfer the cookie dough to a bowl and refrigerate for at least 2 hours or overnight to allow the flavors to meld and the dough to firm up.

Preheat your oven to 325°F (165°C). Line baking sheets with parchment paper or silicone baking mats.

Remove the dough from the refrigerator and let it sit at room temperature for 30-40 minutes to soften slightly.

Using your hands, roll the dough into 1-inch wide balls and place them on the prepared baking sheets about 2 inches apart.

Flatten the dough balls slightly with the palm of your hand.

Bake the cookies in the preheated oven for 16-18 minutes, or until they are just barely beginning to turn golden brown around the edges.

Remove the cookies from the oven and transfer them to a wire rack to cool completely.

Once cooled, store the cookies in an airtight container at room temperature for up to one week. You can also freeze the baked cookies in a zip-lock bag if you want to keep them fresh for longer.