Heat oil in a Dutch oven over medium heat. Add onion and celery. Cover and cook 15 minutes, stirring occasionally. Add water and next 5 ingredients (water through chickpeas); bring to a boil. Add pasta. Cover, reduce heat, and simmer 20 minutes. Stir in Classic Pesto.
I made this as a side dish, but it's more of a main course--it's very hearty and filling. Like others, I used chicken stock instead of water (water-blah). To be honest, it reminds me more of pasta sauce than soup and I don't know if I would make it again. The recipe makes a lot, so this soup and maybe a salad or bread will be plenty.
A very nice soup that reminded me of the kind my Italian grandmother used to make - simple fresh ingredients, a nice touch from the pesto, and strong notes of the aromatics (celery and onion). Next time I would add a little more ditalini, and serve the pesto dolloped directly over individual portions, rather than stirred into the broth. Served with French bread and a big salad.