Clean the duck fat and pan fry well from both side until well browned fat side first. Put the duck in an oven tray and add quartered plums, roast for 9 min @ 180 degrees Celsius. Once duck is out of oven remove juices from tray to a well preheated pan on high heat and reduce together with the Marsala wine. Bring the stock to the boil and mix well with the couscous in a bowl. Add some orange zest and cover for 5 minutes until the couscous is cooked. Meanwhile in a well preheated pan caramelize the onions cut in fine strips until gold in colour and pour in the squeezed orange and balsamic. Allow juices to be absorbed and remove from heat. Serve the couscous as a base with the onions and spinach on it and the duck sliced on top.