Place the whole chicken into a large stockpot, add water or broth, then bring to a gentle simmer over medium heat. Skim off any foam that rises to the surface, and cook for about 30 minutes until the chicken is partially cooked.
Add diced onion, sliced carrots, sliced celery, and minced garlic to the pot. Continue simmering for another 30 minutes, allowing flavors to meld and the chicken to become tender.
Remove the chicken from the pot and set aside to cool slightly. Carefully strain the broth into another container if desired for a clearer soup, or leave the vegetables for added texture.
Shred the cooled chicken into bite-sized pieces, discarding skin and bones. Return the shredded chicken to the broth.
Bring the broth with chicken back to a gentle simmer over medium heat. Season with salt and pepper to taste.
Add the uncooked egg noodles to the simmering broth. Cook for about 8-10 minutes, or until noodles are tender and flavorful.
Once the noodles are cooked, taste the soup and adjust seasoning as needed. Ladle the hot soup into bowls, garnish with chopped parsley, and serve immediately.