Preheat the oven to 350 degrees F (175 degrees C). Grease cookie sheets or line with parchment paper.

Beat butter, white sugar, brown sugar, eggs, and vanilla in a large bowl until light, fluffy, and well combined.

Pulse rolled oats in a food processor until finely ground. Whisk together ground oats, flour, salt, baking powder, and baking soda in a separate bowl.

Gradually add the dry ingredients to the butter mixture, beating just until combined. Fold in chocolate chips and walnuts.

Roll dough into golf ball-sized balls and place about 2 inches apart on the prepared cookie sheets.

Bake in the preheated oven until the edges are lightly golden and the centers are just set, 8 to 10 minutes. Let cookies cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.