Prepare the pitta crisps first by slicing the pitta breads into diagonal strips of about 2 cm wide. Open up each slice to make two pieces and arrange on a baking sheet. Sprinkle with olive oil and season with salt and pepper and bake in the oven (220°C/425°F/gas mark 6) for 15 minutes until crisp all over.
While the pitta crisps are in the oven, start making the soup. Begin by heating the stock and season well with salt and freshly ground black pepper.
Add vegetables and simmer gently for 3-4 minutes until tender then remove from the heat.
Gently stir in the herbs, lemon juice and spring onion and serve piping hot with a few pitta crisps on top.