Cream together margarine, sugar and syrup. In a jug, stir bicarb. or soda into orange juice and add to bowl. Sift flour, baking powder, cocoa and salt and gradually stir into the bowl. Add orange peel. Spoon the mixture (which will be quite sloppy) into a medium sized square tin. Generously sprinkle the top with more sugar. Bake for about 35-40 minutes, until cooked in the centre. Cool briefly in the tin and then turn out onto a wire rack.