Place the squash on a roasting tray and drizzle with 1 tablespoon of the oil. Season with salt and pepper and sprinkle over the cumin seeds. Roast in a preheated oven, 180°C (350°F), Gas Mark 4, for 30 minutes until the squash is tender.
Meanwhile, mix together the coriander, ground cumin, paprika and 2 tablespoons of the oil. Rub the mixture over the swordfish steaks and leave in the refrigerator to marinate for 30 minutes.
Place the couscous in a heatproof bowl. Mix the harissa paste with the boiling stock and pour it over the couscous. Cover the bowl with clingfilm and leave for 5–8 minutes, then fluff the couscous up with a fork to separate the grains. Mix in the lemon juice and remaining oil and season with salt and pepper. Finally, stir in the roasted butternut squash.
Place the marinated swordfish in a very hot griddle pan and cook for 3–4 minutes on each side. Serve immediately with the warm couscous.