Heat the oven to 200°C (Gas Mark 6). Cut the stem off the broccoli, then slice it as thinly as you can and place in a bowl with one tablespoon of the oil, all the lemon zest and half of the juice, the chilli flakes (if using) and a pinch of salt. Toss to coat, then set aside.
Next, cut the head of the broccoli into small florets and place them in a roasting tin. Drizzle the florets with a tablespoon of oil, then season with salt and pepper and turn until evenly coated. Roast in the hot oven for 10 minutes.

When 10 minutes is up, take the tray out of the oven. Tear the bread into bite-sized chunks and add them to the tray, together with half a tablespoon of the oil. Toss the bread and broccoli together, then put the tray back in the oven for another 10 minutes.
While the bread and broccoli are cooking, make the dressing; put the walnuts into a pestle and mortar (or the small bowl of a food processor), together with a pinch of salt, then crush in the garlic cloves and pound or blend into a rough paste. Add the remaining lemon juice and the rest of the oil and mix again to make a dressing.

When the broccoli and bread are ready, tip them into a large serving dish and add the broccoli stems. Add the prepared tomatoes and the walnut sauce, then rip over the basil leaves and toss everything together to combine, before serving.