Preheat oven to 350°.
Cream together butter, sugar and brown sugar.
Add eggs one at a time, beating after each addition.
In a separate bowl, combine flour, cocoa, baking soda and salt. Gradually mix in to batter.
Add oats slowly; dough will become stiff. Fold in peppermint baking chips.
Drop by tablespoonfuls onto an ungreased baking sheet.
Bake for 11 minutes until set; cool 2 minutes on cookie sheet before transferring to a wire rack to cool completely.