Step 1

Combine chicken broth, onion, carrots, celery, and salt in a large pot. Bring to a boil; reduce heat and simmer, uncovered, until flavors combine, about 30 minutes. Discard onion, carrot, and celery from the broth.

Step 2

Bring broth to a boil. Add meatballs. Reduce heat and simmer until meatballs are heated through, about 10 minutes. Stir in tomatoes, spinach, olive oil, lemon juice, Parmesan cheese, garlic, and dried basil. Simmer until flavors combine, 15 to 20 minutes.