Preheat oven to 425°F and line a sheet pan with parchment paper.
In a small bowl combine breadcrumbs and milk. Let sit for about 5 minutes until the milk is absorbed.
In a large bowl combine ground turkey, the soaked breadcrumb mixture, egg, parmesan, grated onion, garlic, Italian seasoning, salt, black pepper, and parsley. Mix gently until just combined, being careful not to overmix. Let the mixture rest 5–10 minutes so the breadcrumbs fully hydrate and the meatball mixture holds together. Roll the mixture into small meatballs about ¾ inch wide, roughly 1 tablespoon each, and place them on the prepared sheet pan.
Bake the meatballs for 8–10 minutes, just until they are set. They do not need to be fully cooked yet since they will finish cooking in the soup.
While the meatballs bake, heat olive oil in a large Dutch oven or soup pot over medium heat. Add onion, carrots, and celery and cook 5–6 minutes until softened. Stir in grated garlic and cook 30 seconds until fragrant.
Pour in the white wine and scrape the bottom of the pot to loosen any browned bits. Simmer 2–3 minutes until the wine reduces by about half.
Add chicken broth and the parmesan rind and bring the soup to a gentle boil. Add the baked meatballs and reduce heat to a steady simmer. Cook 10 minutes so the meatballs finish cooking and flavor the broth.
Stir in the acini de pepe and cook 8–10 minutes until the pasta is tender.
Add spinach and cook just until wilted. Remove the parmesan rind, stir in lemon juice and fresh parsley, and taste for seasoning. Adjust salt and black pepper as needed before serving.
Serve hot with extra grated parmesan if desired.
