Combine brownie mix, eggs, and water.
Spread batter in glass baking dish.
Cook on bake (6) for 8 minutes.
Cook on high (9) for 2 to 3 minutes or until brownies are dry on top.
Combine butter and chocolate pieces in a glass mixing bowl.
Cook on high (9) for 1 minute or until melted.
Stir in marshmallows and peanuts, blend well.
Top brownies with frosting.
Allow to cool.
Cut into bars.