Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large mixing bowl, combine the chocolate chip cookie mix, melted butter, egg, and vanilla extract. Stir until the dough comes together and is evenly mixed.
Fold in the chopped walnuts, rolled oats, and mini chocolate chips until evenly distributed throughout the dough.
Using a tablespoon or cookie scoop, drop rounded dough balls onto the prepared baking sheets, spacing them about 2 inches apart.
Bake the cookies in the preheated oven for 10 to 12 minutes, or until the edges are golden brown and the centers are set.
Remove the cookies from the oven and allow them to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.