Spray a half sheet jelly roll pan (13x18") with non stick cooking spray. Preheat oven to 350 degrees.
Cream peanut butter, butter, and sugars in a large mixing bowl. Beat in the eggs and vanilla. Stir in flour, baking soda, salt, and oats.
Mix together well and press dough evenly into the prepared pan.
Bake at 350 for 15 minutes, or until just barely set in the middle. Don't over bake.
While bars are still warm, drop spoonfuls of peanut butter on top, and spread evenly.
Cool completely then spread chocolate frosting over the peanut butter.
For frosting, beat butter and cocoa in a mixing bowl until smooth. Add powdered sugar, salt, and vanilla. Add enough milk to make a spreadable consistency and beat till smooth and creamy.