Pour the olive oil to a saucepan and place over a medium heat. Add the onions to the pan and cook gently for 5 minutes taking care to soften but not colour the onion.
Add the courgette, pepper and garlic to the saucepan and continue to cook for a further minute. Then add the couscous, lemon zest and juice and stir well to combine.
Pour the vegetable stock over the couscous and take the pan off the heat. Cover with a lid and leave the couscous to steam for 5 minutes.
Meanwhile place a non-stick frying pan over a medium-high heat and add the sunflower oil. Season both sides of the fish and place skin side down in the pan. Cook the fish for 3 minutes on this side then turn. Add a knob of butter, cook for a further 2 minutes and remove from the heat.
The couscous should now have absorbed all the stock, Season with salt and pepper, add the parsley and fork through the butter.
Spoon the couscous onto warm plates and place a fillet of hake on each. Serve immediately.
We have used fresh Hake fillets in this recipe, however you can easily substitute with other white fish. Sea bass or sea bream work just as well.