Preheat the oven to 210°C/gas mark 6. Divide the vegetables between two wide roasting tins and mix with mustard and oil, then season to taste. Roast for 20 minutes then turn over and roast for another 15-20 minutes, until golden brown.
Meanwhile, place the couscous in a heatproof bowl and pour over the hot vegetable stock. Cover and leave to sit for 5 minutes or until the stock is completely absorbed. Stir through the lemon juice, extra virgin olive oil and parsley. Season to taste.
Once the vegetables are cooked, stir them through the couscous and serve.