ON THE DAY Preheat the oven to 150°C/300°F/gas 2. In a large roasting tray, mix the harissa with 1 tablespoon each of red wine vinegar and olive oil and a pinch of sea salt and black pepper. Add the tomatoes on the vines, trim and add the whole spring onions, then break up the garlic, squash the unpeeled cloves and add to the tray. Gently toss together, roast for 1 hour, then remove.
Squeeze the soft garlic flesh out of the skins on to a board, finely chop with the spring onions and most of the herb leaves, then scrape into a large pan. Pour the tomatoes and all the juices from the tray through a coarse sieve into the pan, pushing it all through with the back of a spoon. Keep aside.
TO SERVE Heat up the sauce while you cook the broad beans in a large pan of boiling salted water for 2 minutes. Remove with a slotted spoon, pinching the skin off any larger beans, if you like, while you cook the orzo in the large pan of boiling salted water according to the packet instructions. Drain, pour into the sauce with the beans and turn the heat off, letting the orzo suck up all that flavour. Transfer to a large serving bowl, pick over the remaining herbs and finish with a drizzle of extra virgin olive oil. Serve hot or at room temperature.