Lightly butter 8 inch round or square pan; set aside.
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.
Stir in frosting, marshmallows and peanuts until blended. (Mixture will become very thick; knead if necessary.)
Press mixture evenly in buttered pan.
Refrigerate until set.
Cut into squares.
Cover tightly; store in refrigerator.