In a large bowl cream together the copha, white sugar and brown sugar until smooth. Beat in the eggs one at a time, then stir in the orange zest, molasses and vanilla. Combine the flour, bicarb soda and salt; stir into the molasses mixture until well blended. Mix in oats.
Divide the dough into halves, and shape into long logs about 5cm in diameter. Wrap in waxed paper and refrigerate for at least 8 hours or overnight.
Preheat the oven to 180 degrees C. Slice chilled dough into rounds about 5mm thick. Place 5cm apart onto ungreased baking trays.
Bake for 11 to 13 minutes in the preheated oven, until the bottoms are lightly browned. Cool on the baking pan for a minute before removing to wire racks to cool completely.