Preheat oven to 350F and prep a cookie tray with parchment paper.
In a large bowl add box cake mix, oil, eggs and mix by hand with a spatula until well blended (about 30-60 seconds).
Fold in pecans just until combined, then using a 1 ½ tablespoon cookie scoop, leaving a couple of inches between each ball, add to your baking sheet. You can add a whole pecans on top of the cookie, if desired.
For chewy cookies, bake for about 9 minutes.
Cool on the cookie sheet for about 10 minutes before transferring to a wire rack.
Use a fresh or cooled cookie sheet before starting the next batch so the cookies do not start to spread too soon.
Notes
Expect Sticky Dough: Cake mix cookie dough is thicker and stickier than traditional cookie dough. A cookie scoop makes portioning it much easier.
Chewy Cookies: Pull them from the oven when the edges are set but the centers still look soft. They'll continue to firm up on the baking sheet.
Check for Doneness: Ovens vary and these cookies bake quickly, so start checking around 8 minutes. They should look soft but not wet in the center.
Don't Overmix: Stir the cake mix, oil, and eggs just until well blended, then gently fold in the chopped pecans to keep the cookies soft and chewy.
Use a Cool Baking Sheet: Let the cookie sheet cool completely or use a fresh one before starting the next batch. A hot baking sheet can cause the dough balls to begin spreading before they reach the oven.
Keep the Cookies Even: A 1 ½ tablespoon cookie scoop helps keep the cookies a similar size, so they bake at the same rate.
Dough Texture: Cake mix cookie dough is thicker and stickier than traditional cookie dough. A cookie scoop makes portioning it much easier.