Lightly butter 8-inch round or square pan. In large microwave-safe bowl, combine peanut butter chips and oil. Microwave on HIGH for 1 to 1 1/2 minutes or until chips are melted. Stir until smooth.
Add frosting, marshmallows and peanuts; blend well. (Mixture will become very thick; knead if necessary). Press mixture evenly in buttered pan. Refrigerate 30 minutes or until set. Cut candy into squares. Store in refrigerator.