In a bowl, combine the ground chicken, breadcrumbs, Parmesan cheese, egg, basil, minced garlic, salt, and black pepper. Mix until well combined and form into small meatballs.
In a large pot, heat the olive oil over medium heat. Add the onion, carrots, and celery, and cook until they begin to soften, about 5 minutes.
Add the chicken meatballs to the pot and cook until they are browned on all sides, about 8 minutes. Make sure not to overcrowd the pot; you may need to do this in batches.
Pour in the chicken broth and bring to a boil. Reduce the heat to a simmer and cook for 10 minutes.
Stir in the escarole, dried thyme, and red pepper flakes if using. Let the soup simmer for another 5 minutes.
Add the pastina to the pot and cook according to the package instructions, generally about 6-7 minutes, until the pasta is tender.
Taste and adjust seasoning if necessary. Serve hot, garnished with grated Parmesan cheese.
