In a large 8-quart stockpot, heat the olive oil over medium-high heat. Sear the chicken pieces in batches for 4-5 minutes per side until the skin is golden brown. Remove the chicken and set aside on a plate.
Reduce the heat to medium. Add the onion, carrots, celery, and leeks to the rendered fat in the pot. Sauté for 6-8 minutes, stirring occasionally, until the vegetables are softened and the onions are translucent.
Add the minced garlic and cook for 60 seconds until fragrant.
Return the chicken pieces to the pot along with any accumulated juices. Add the chicken broth, thyme, rosemary, bay leaves, salt, and pepper.
Bring the liquid to a boil, then immediately reduce the heat to low. Cover and simmer gently for 60 minutes, ensuring the chicken is tender and fully cooked.
Use tongs to remove the chicken from the pot and transfer it to a cutting board. Let it cool for 10 minutes, then shred the meat into bite-sized pieces, discarding the skin and bones.
Remove and discard the bay leaves from the broth. Bring the soup back to a light boil over medium heat.
Add the egg noodles to the pot and cook for 8-10 minutes, or until the noodles are al dente.
Return the shredded chicken to the pot. Stir in the fresh parsley and lemon juice. Taste and adjust salt and pepper before serving hot.