Bring the sugar, milk, butter and cocoa to a boil in a medium saucepan over medium heat, stirring occasionally, then stop stirring and let it boil for 1 minute. Remove from the heat. Stir in the oats, peanut butter, vanilla and salt.
Drop teaspoonfuls of the mixture onto the prepared baking sheet, and let sit at room temperature until cooled and hardened, about 30 minutes. Refrigerate in an airtight container for up to 3 days.