Combine the ground turkey, egg, breadcrumbs, Parmesan cheese, 1 teaspoon Italian seasoning, salt, and pepper in a mixing bowl. Mix gently with your hands until just combined, then roll the mixture into small meatballs about 1 inch across.
Heat the olive oil in a large pot over medium heat. Add the meatballs in a single layer and cook, turning occasionally, until browned on all sides. Remove them from the pot and set aside.
Add the diced onion to the same pot and cook for 3 minutes until it softens. Stir in the minced garlic and cook for 1 minute more.
Pour in the chicken broth, diced tomatoes, and remaining 1 teaspoon Italian seasoning. Bring the mixture to a simmer.
Return the meatballs to the pot and let everything simmer gently for 10 minutes until the meatballs are cooked through.
Stir in the fresh spinach and cook for 2 minutes until it wilts. Taste and adjust salt or pepper if needed before serving.