Preheat your oven to 350°F (175°C) and line a large baking tray with parchment paper.
Spread the pecans on the baking tray and toast them in the oven for about 6 minutes. Remove from the oven and let them cool completely before chopping.
In a medium bowl, mix the flour, oats, baking soda, and salt. Set this mixture aside.
In a large mixing bowl, beat the butter on high speed for about a minute until creamy.
Add the sugar, egg, and vanilla extract to the butter. Beat until well combined, scraping the sides of the bowl occasionally.
Stir in the flour and oat mixture until fully combined. Gently fold in the chopped pecans.
Drop rounded teaspoons of dough onto the prepared baking tray, spacing them about 2 inches apart. Bake for 8-10 minutes or until the edges are lightly browned.
Let the cookies cool for a few minutes, lightly flatten them with a spatula, and transfer to a wire rack to cool completely.
Store the cookies in an airtight container for up to a week or freeze for up to a month.
Notes
For extra flavor, you can add a pinch of cinnamon or nutmeg to the dough.