Stir together sugar, cocoa and milk in 4-cup glass measure or medium microwave-safe bowl. Microwave on HIGH 1 to 1-1/4 minutes or until boiling, stirring once.
Stir in peanut butter and vanilla until blended. Stir in oats until combined. Drop by spoonfuls onto a waxed paper-lined plate to make 6 cookies. Cool in freezer 10 minutes before serving.