Soak the barley for a couple of hours in advance.
Heat the oven to 200C (180C fan)/390F/gas 6.
Put the onion, pepper, aubergine/courgette and tomatoes on a baking tray, spoon over 4 tbsp of oil, sprinkle with salt and toss well so all the veg glisten. Roast for 25 minutes, stirring occasionally, or until the veg are very soft and golden at the edges; if they are also a bit mushy, that is fine
While the veg are roasting, boil the pearl barley in plenty of salted water for about 15 mins or until al dente, then drain and spread on a plate to cool slightly.
Finely chop the herbs and put them in a large bowl with the lemon zest, 3 tbsp of oil, a teaspoon of red-wine vinegar and, if you wish, a teaspoon of sweet vinegar.
Add the pearl barley, roast veg and green beans and toss well.