In a large bowl, combine the turkey, bread crumbs, 3 eggs, 1/4 cup parmesan and 1/2 teaspoon each salt and pepper. Roll the mixture into 3/4-inch meatballs and set aside.
In a large pot, heat the olive oil over medium heat. Add the onion and cook, stirring occasionally, until softened and slightly browned, about 8 minutes. Pour in the broth, increase the heat to high and bring to a boil. Add the meatballs and return to a boil. Lower the heat and simmer until the meatballs are cooked through, about 10 minutes. Stir in the escarole.
In a small bowl, lightly beat the remaining 3 eggs with 2 tablespoons water and 1/4 teaspoon each salt and pepper. Slowly drizzle the egg mixture into the simmering broth, pushing the meatballs and escarole aside. Stir in the remaining 1/4 cup parmesan cheese and season with salt and pepper. Serve with more parmesan and the lemon wedges.