Line an 9"13" or a 8"x8" (for thicker fudge) pan with foil; coat with cooking spray.
Place the chocolate chips and condensed milk in a large microwave safe bowl. Microwave for 1 minute on High power then stir. If the morsels aren't fully melted and blended, continue microwaving in 15 second intervals. Add in the vanilla extract and stir until smooth. Now add the mini marshmallows and nuts, gently stir to combine.
Press the fudge into the prepared pan. Refrigerate until ready to serve. Use the foil to lift the fudge out of the pan and cut into bite sized pieces, then serve.