Tip the couscous into a heatproof bowl and just cover with boiling water. Cover with clingfilm and leave to stand for 5 minutes. Fluff up with a fork, then stir in the oil to separate the grains. Transfer to an ovenproof dish, stir in the preserved lemon rind, season with pepper and scatter over the butter. Cover with a damp piece of greaseproof paper and place in a preheated oven, 180°C (350°F), Gas Mark 4, for 10 minutes until heated through.
Meanwhile, heat the olive oil in a heavy-based frying pan over a medium heat, add the seafood and cook for 3–4 minutes. Add the harissa, season and stir in most of the coriander.
Pile the couscous in a mound on a shallow serving dish. Spoon the seafood over the couscous and serve garnished with the remaining coriander.