Preheat the oven to 350°F (175°C) so it reaches the correct temperature before the cookies are baked.
Place the softened butter, packed brown sugar, and granulated sugar in a large mixing bowl. Beat the ingredients together until the mixture becomes pale, smooth, and fluffy.
Add the room-temperature eggs and vanilla extract to the creamed butter mixture. Continue beating until fully incorporated and slightly glossy.
In a separate medium bowl, whisk together the all-purpose flour, baking soda, cinnamon, and salt until evenly blended.
Gradually add the dry mixture to the wet ingredients. Stir until the flour is incorporated and a cohesive cookie dough develops.
Fold the old-fashioned oats into the dough, distributing them evenly throughout. Add the chocolate chips and pecan pieces, then mix only until the additions are uniformly combined.
Using a 1½-tablespoon cookie scoop, portion equal mounds of dough onto an ungreased cookie sheet. Leave approximately 2 inches of space between each portion.
Bake for 10–12 minutes, or until the outer edges are beginning to turn golden brown.
Remove the cookies from the oven and carefully transfer them to a wire cooling rack. Let them cool completely before serving or placing them in storage.