Heat your oven to 200°C/Fan 180°C/Gas 6. Peel the onion and slice it into thick wedges. Chop the courgette into half-moons around 1cm thick. Halve the pepper. Scoop out the seeds and white bits. Chop into small chunks, the same size as the courgette.
Put all the veg in a bowl. Add 2 tsp olive oil and a pinch of salt and pepper. Toss to mix. Spread out in a baking tray. Roast for 30 mins, till the veg are tender and a little charred.
While the veg roast, quarter the cherry tomatoes. Peel and grate or crush the garlic. Finely chop the coriander and parsley, leaves and stalks.
Warm 1 tsp olive oil in a small pan. Add the garlic and 1 tsp each ground cumin and smoked paprika. Cook and stir for 1 min till the garlic is golden.
Add the tomatoes and most of the parsley and coriander. Season with salt and pepper. Gently cook for 10 mins, stirring now and then, till the tomatoes start to break down and form a chunky sauce. This is your chermoula. When it's ready, put to one side with the lid on.
When the veg have roasted for 30 mins, shuffle them across to one side of the tray. Lay the cod fillets in the space you've made on the tray, skin-side down. Roast for 10-15 mins till the fish is white, opaque and flakes easily when pressed with a fork.
While the cod cooks, put the couscous in a heatproof bowl. Pour in 150ml boiling water. Cover the bowl with cling film or a plate. Set to one side to soak. When the cod is nearly ready, put the chermoula over a low heat and warm through for 2-3 mins.
Tumble the roast veg into the couscous, season with a little salt and pepper and toss to mix. Heap the couscous onto warm plates. Top with the roast cod and the tomato chermoula, garnished with the last of the chopped herbs.