Place couscous, spring onions, lemon zest and cumin in a large heatproof bowl. Bring water to the boil in a small saucepan with the pinch of saffron in it. Pour over the couscous, cover the bowl with plastic wrap and set aside 10 minutes.
Add the herbs and cherry tomato halves to the couscous and fluff with a fork. Season with salt and pepper.
Tear four sheets of foil or baking paper about 45cm long. Brush the centre of each piece with olive oil and place a quarter of the couscous on each. Top with a fish fillet, drizzle with a little more olive oil, squeeze over some lemon juice and season with salt and pepper. Wrap up the fish in the foil, folding the edges to seal well.
Place the packages on a baking sheet and cook in the preheated oven for 15-20 minutes. The parcels should puff up a little. Serve on warmed plates with lemon wedges.