Cook acini de pepe until al dente. Drain and set aside.
Add chicken broth to a large pot and bring to a boil. Turn down heat to medium low.
Tear bread into tiny pieces by hand and add to a large bowl. Add in ground chicken, egg, garlic, onion powder, pepper and ¼ cup Parmesan cheese. Mix together with clean hands. Form 1 tbsp of the mixture into balls by hand.
Place meatballs in simmering broth, cover, and bring back to a boil. Turn down the heat to medium low, cover, and cook for 15 to 20 minutes, until meatballs are cooked through.
Stir in baby spinach and acini de pepe pasta. Cook until spinach is wilted and pasta is heated, about 3 to 5 minutes.
To serve, ladle into bowls and top with remaining Parmesan cheese.