Rapido Meatball Soup

1
Heat 2 tablespoons oil in a 5- to 6-quart pot over high heat until hot but not smoking, then cook onions, garlic, celery, and carrots, stirring occasionally, until onions are pale golden, about 4 minutes. Stir in broth and water and bring to a boil, covered.
2
Meanwhile, heat remaining 2 tablespoons oil in a 12-inch heavy skillet over high heat until hot but not smoking, then sauté meatballs (do not thaw if frozen), turning occasionally, until browned all over, about 3 minutes.
3
Add meatballs to soup along with beans and briskly simmer, covered, stirring occasionally, until vegetables are tender and meatballs are heated through, about 15 minutes.
4
Stir in spinach, cheese, salt, and pepper and simmer, uncovered, until spinach is wilted, about 1 minute.