Preheat the oven to 350°F (175°C). Line a large baking tray with parchment paper.

Spread the pecans on the lined tray and toast them in the oven for about 6 minutes, until fragrant. Remove and cool completely, then roughly chop.

In a medium bowl, whisk together the flour, oats, baking soda, and salt. Set aside.

In a large bowl or stand mixer, beat the softened butter on high for about 1 minute until creamy.

Add the sugar, egg, and vanilla. Beat until evenly combined and smooth.

Fold the dry mixture into the butter mixture until just combined, avoiding overmixing.

Gently fold in the chopped toasted pecans.

Drop rounded teaspoons of dough about 2 inches apart on the prepared tray.

Bake for 8–10 minutes until edges are lightly browned but centers still look soft.

Let the cookies rest on the tray for a few minutes, then gently flatten each cookie with a spatula.

Transfer cookies to a wire rack to cool completely.