In a large pot, bring water or chicken broth to a boil. Add the 1 pound boneless, skinless chicken breasts and cook for 15-20 minutes, or until fully cooked. Shred the chicken using two forks and set aside.
In the same pot, melt 2 tablespoons unsalted butter over medium heat. Add the diced 1/2 cup onion, 2 medium carrots, and 2 stalks celery. Sauté for 5-7 minutes, or until the vegetables are softened. Add the minced 2 cloves garlic and cook for another minute until fragrant.
Add 4 cups chicken stock, 1 teaspoon dried thyme1 teaspoon Kosher salt, and 1/2 teaspoon black pepper to the pot. Stir to combine and bring the soup to a simmer.
Stir in the 8 ounces egg noodles and cook for 7-9 minutes, or until the noodles are tender.
Add the shredded chicken to the soup and let it simmer for an additional 5 minutes.
Taste the soup and adjust seasoning if needed. Garnish with fresh parsley before serving.