Preheat your oven to 350°F (175°C) to ensure even baking.
Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a large mixing bowl, combine the refrigerated chocolate chip cookie dough and oats. Mix well with a spatula.
Press the cookie dough mixture evenly into the bottom of the prepared pan to form the crust.
In a microwave-safe bowl, combine the sweetened condensed milk and semisweet chocolate chips. Microwave in 30-second intervals, stirring in between, until melted and smooth. Stir in vanilla extract.
Pour the melted fudge mixture over the cookie dough crust, spreading evenly with a spatula.
Sprinkle the mini M&M's and Reese's peanut butter chips over the fudge layer, pressing in slightly to stick.
Bake for 25-30 minutes, until edges are golden and center is set. Avoid overbaking.
Allow bars to cool completely in the pan on a wire rack. Lift out using parchment paper and cut into squares.