Heat some oil in a large saucepan or casserole dish, and add the diced onion, carrot and celery. Cook over a medium heat for a few minutes, stirring regularly, then add the diced peppers, courgette, garlic, and chopped kale. Cook for a further 5 minutes.
Add the tin of chopped tomatoes to the pan, along with the drained cannellini beans, vegetable stock, and dried pearl barley. Also add the oregano, thyme, pesto, and plenty of black pepper. Mix well to combine. Cover the pan with a lid, just leaving a crack for the steam to escape, and turn the heat down fairly low so the soup is simmering gently. Allow it to cook, stirring occasionally, for around an hour, or until the pearl barley is soft.
If the soup has reduced at all, you may wish to add another cup or two of water at this point, to help is stretch further. The soup should serve at least 4 people, but could serve up to 6 people, if you add some extra liquid.
To make the croutons, tear some crusty bread into large pieces, and toss in a tablespoon of oil with some salt and pepper. Bake for around 10 minutes at 190°C (Gas Mark 5 / 375°F), until golden brown and crispy.
Serve the soup warm, topped with the crispy croutons, a drizzle of extra virgin olive oil, and some fresh parsley.