Heat oven to 350°F. Spray 15x10x1-inch baking pan with nonstick cooking spray.* Place melted butter in large bowl. Reserve 3 tablespoons of the cake mix; set aside. Add remaining cake mix to butter; blend well. Add egg; mix well. Stir in oats. Press 2/3 of cake mix mixture (about 2 1/2 cups) in bottom of sprayed pan.
Place frosting in medium microwave-safe bowl; microwave on HIGH for 1 minute. Add reserved 3 tablespoons cake mix; stir until large lumps disappear.
Drizzle half of frosting mixture over cake mix mixture in pan; spread evenly. Sprinkle with chocolate chips and pecans. Drizzle with remaining frosting mixture. Crumble remaining cake mix mixture over frosting mixture.
Bake at 350°F. for 25 to 30 minutes or until top is golden brown and edges are bubbly. Cool 1 1/2 hours or until completely cooled. Cut into bars.