Heat the oil in a large saucepan, add the onion and garlic and cook for 2–3 minutes until softened.
Pour over the stock, bring to the boil and add the potatoes. Cover, reduce the heat and simmer for 10 minutes.
Add the carrots, courgettes and tomatoes, re-cover and simmer for a further 10 minutes. Stir in the peas and cook for 4–5 minutes or until all the vegetables are tender. Season to taste with salt and pepper.
Ladle the soup into large warmed bowls and serve each topped with a tablespoon of pesto, along with crusty bread rolls, if liked.