In a large bowl, gently stir together turkey, bread crumbs, egg, 1 teaspoon salt, 1 teaspoon pepper, and garlic powder until well combined. Shape mixture into 1¼-inch balls.
In a 4-to 6-quart cast-iron Dutch oven, heat 2 tablespoons oil over medium heat. Add half of meatballs; cook, turning occasionally, until lightly browned, about 6 minutes. Remove meatballs using a slotted spoon, and let drain on paper towels. Repeat procedure with remaining 2 tablespoons oil and remaining meatballs.
Add carrots, onion, and celery to pot; cook over medium heat, stirring occasionally, until softened, 8 to 10 minutes. Stir in broth, 4 cups water, thyme, remaining 1½ teaspoons salt, and remaining 1 teaspoon pepper, and bring to a boil over medium-high heat. Stir in meatballs and noodles; return to a boil. Reduce heat, and simmer until noodles are tender and meatballs are cooked through, about 12 minutes. Stir in lemon juice. Garnish with thyme, if desired.
Recipe by Southern Cast Iron at https://southerncastiron.com/turkey-meatball-noodle-soup/