Preheat oven to 375F/190C.

Boil some water, put the couscous in a heatproof bowl and pour over enough boiling water to just cover the couscous. Set aside, covered, while you prepare everything else.

Clean out the fish if not properly cleaned before and score each twice on each side. Lay in a baking dish big enough for the fish to lie flat.

Finely dice the onion. Remove the chard stems from the leaves and finely chop the stem and shred the leaves. Finely chop the garlic and roughly chop the parsley.

Warm the oil in a medium-large skillet and soften often onion, stirring now and then. If it starts to brown, you probably need to either reduce the heat or add a little more oil or both. After around 3min, add the chard stalks and garlic. After another approx 5min, when the onion is translucent and the chard stalks appear to be softening, add the chard leaves and cook, stirring, so they wilt down.

Remove the pan from the heat and add the parsley, lemon juice and zest, and couscous and stir all so it is well mixed.

Divide the mixture between the cavities of the two fish and press in well.

Bake for approx 20min until the fish are cooked through.