Combine half the oil with the lemon juice, spices, chilli flakes, salt and half the coriander in a small bowl. Rub mixture all over salmon.
Heat a large frying pan over high heat. Cook salmon, skin-side down, for 2-3 minutes or until skin is crisp. Reduce heat to medium. Turn salmon. Cook for 3-4 minutes or until cooked to your liking.
Meanwhile, combine boiling water, stock cube and remaining oil in a heatproof bowl. Stir in couscous. Cover tightly with foil. Stand for 5 minutes or until water is absorbed. Fluff couscous with a fork. Stir in lemon rind and remaining coriander. Serve salmon with couscous and yogurt.