Preheat oven to 180 degrees C. Grease baking trays.
In a large bowl, cream together the sugar, margarine and olive oil until smooth. Stir in the vanilla and egg replacer. In another bowl combine the flour, cocoa and baking powder then stir into the creamed mixture. Fold in the chocolate pieces. Cover and chill dough for 10 minutes.
Divide the dough into two equal pieces. Roll each piece into a log about 22cm long. Place the logs onto the prepared baking trays about 10cm apart. Flatten each one down to 3cm thickness.
Bake in the preheated oven for 20 to 25 minutes or until firm. Cool on trays for 15 minutes before removing to wire racks to cool completely.
Transfer the loaves to a cutting board. Using a serrated bread knife, slice each loaf crosswise into 2cm slices. Return slices to the baking tray and bake for an additional 8 to 10 minutes on each side, until dry and lightly toasted. Cool completely before storing in an airtight container.