Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
In a large bowl, cream together the shortening, margarine, white sugar and brown sugar until smooth. Beat in the eggs one at a time, then stir in the peanut butter and vanilla. Combine the flour, cocoa, baking powder, baking soda and cream of tartar; stir into the sugar mixture. Mix in the oats, walnuts (if desired) and chocolate chips. Drop by rounded spoonfuls onto the prepared cookie sheets.
Bake for 8 to 10 minutes in the preheated oven. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.