1. Put the couscous in a bowl. Pour the boiling stock on top and leave the couscous to soak, covered, for 20 minutes.
2. Peel and slice the onion into strips.
3. Grate the peel. Peel the orange and cut into segments, saving the flesh, and squeeze, collecting the juice.
4. Filling pak choi: Heat the olive oil, glaze the onion in the oil and pour in the orange juice (approx. 50 ml). Add the sultanas and reduce the liquid by half. Stir in the couscous with 1 tablespoon of chopped walnuts, the orange zest and freshly ground pepper to taste.
5. Blanch the pak choi, stems side down, in plenty of boiling water for 2-3 minutes. Rinse them with cold water and place on a clean tea towel.
6. Spread the filling over the centre of the pak choi leaves, fold the sides inwards and roll up from the stem. Place the packets in a casserole dish. Pour in 100 ml of vegetable stock and cook the packets over low heat until tender, 5-8 minutes.
7. Toast the remaining tablespoon of chopped walnuts in the margarine and sprinkle over the packets. Enjoy!