Preheat the oven to 200ºC, gas mark 6. Lightly butter a small ovenproof dish and place the cod fillets inside. Mix together the pesto and tomatoes and spoon on top of the fillets. Bake for 15 minutes until cooked through.
Meanwhile, cook the potatoes in a large pan of boiling water for 13–15 minutes. Add the peas and cook for a further 2 minutes until the potatoes are tender. Drain well and return to the pan.
Add a little butter to the pan and lightly crush the potatoes and peas using a masher. Stir in the lemon zest and juice, and season to taste.
Divide the potato mixture between four plates and top with the cod and tomato-pesto mixture, spooning over any baking juices.
Cook’s tip
For a gluten- and dairy-free version of this dish, swap the butter for olive oil and use Sacla’ Free From — Basil Pesto.
