Heat the oil in a large saucepan and cook the spring onions and celery for 2 minutes. Add the garlic and cook for a further minute. Add the potatoes, tomatoes, herbs and stock. Cover and simmer for 15 minutes.
Meanwhile, take the spaghetti and lay over a tea towel. Roll the tea towel up. Hold the pasta at both ends at the edge of the work surface. Pull the tea towel over the edge in a really quick movement. This will cleverly break the pasta into small even lengths.
Stir the pasta into the soup with the beans, simmer for 5-8 minutes. Season with black pepper and stir in the basil leaves and then serve with some crusty bread and a few Parmesan shavings, if you like.