Preheat your oven to 220°C/Fan 200°C/Gas 7. Fill and boil your kettle. Trim the ends off the French beans and cut the beans in half. Halve the cherry tomatoes. Tumble onto a large baking tray lined with baking paper. Drizzle over 1 tbsp olive oil and season with salt and pepper. Toss to coat, then spread the veg out in a single layer on the tray.

Make 2 gaps in the veg and add the cod fillets, skin-side down. Dollop 1 tbsp pesto onto each fillet and spread it to coat them. Slide the tray into the oven for 12 mins. The veg will be lightly charred and bursting and the cod cooked through. Check by lightly pressing the thickest part of a fillet with the back of a fork. It should be opaque and flaky. Cook a little longer if needed.

Meanwhile, scrub the potatoes and chop them into halves or quarters so they're all roughly the same size. Pop them into a large pan with a pinch of salt. Cover with boiling water and simmer for 12- 15 mins till tender when pierced with a sharp knife. Drain and tip back into the pan.

While the fish and potatoes cook, peel and thinly slice the red onion. Pop it into a bowl. Zest in the lemon and squeeze over the juice from one half. Add a pinch of salt and stir. Set aside.

Finely chop the parsley. Drain the cooked potatoes if you haven't done so already. Add the onion to the pan of potatoes, along with its lemon marinade and the chopped parsley. Toss to mix. Divide the pesto cod between 2 warm plates and serve with the beans and tomatoes, the onions and potatoes, and wedges of lemon for squeezing.