Step 1: Preheat your oven to 375°F (190°C). Line baking sheets with parchment paper or silicone baking mats.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Set aside.
Step 3: In a large bowl, using an electric mixer, cream together the softened unsalted butter, light brown sugar, and granulated sugar until light and fluffy (about 2-3 minutes).
Step 4: Beat in the eggs one at a time, mixing well after each addition. Then, stir in the vanilla extract until just combined.
Step 5: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.
Step 6: Fold in the old-fashioned rolled oats and chopped pecans until evenly distributed.
Step 7: Drop rounded tablespoons of dough onto the prepared baking sheets, leaving about 2 inches between each cookie.
Step 8: Bake for 10-12 minutes, or until the edges are golden brown and the centers are still slightly soft.
Step 9: Remove the cookies from the oven and let them cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.