Line a large sheet pan with parchment paper. Set aside.
Bring sugar, butter, milk and cocoa powder to a boil in a medium saucepan over medium heat, stirring occasionally. Boil for 1 minute, stirring constantly.
Remove from heat and stir in peanut butter and vanilla. Then add oats, stirring well until completely incorporated.
Scoop 1-2 tablespoon mounds of the cocoa mixture onto the prepared sheet pan (a small cookie scoop or spoon works well). Cool completely before serving.