Preheat the grill to medium-high. Heat 1 teaspoon of the olive oil in a large pan over a medium heat. Add the onion and cook gently until translucent (not golden).
Pour in the stock and bring to a simmer. Add the peas, beans, courgette and tomatoes, and simmer for about 5 minutes until just tender. Meanwhile, brush the ciabattas with the remaining oil and toast under the grill.
Divide the soup between 6 bowls. Stir half a tablespoon of pesto into each and serve with a ciabatta crouton on the side.