3 tablespoons olive oil
2 cups chopped onions
2/3 cup chopped carrot
2/3 cup chopped celery
3 1/2 cups (or more) water
2 to 2 1/2 cups cooked white beans with 3/4 cup reserved cooking liquid (see Cannellini Beans with Garlic and Sage)
1 large tomato, seeded, finely chopped
1 cup small pasta (such as farfalline)
1/3 cup chopped green onions (white and pale green parts only; about 2)
Extra-virgin olive oil (for drizzling)