Chop the carrots, celery, and onion into small, even pieces to ensure they cook uniformly and release their flavors fully during sautéing.
Heat the large heavy-bottomed pot over medium heat, then add a splash of oil and sauté the aromatics until they become fragrant and translucent, about 5-7 minutes. You'll notice a sweet aroma and the vegetables will start to soften.
Add the chicken broth to the pot and increase the heat to bring it to a gentle simmer. Carefully place the chicken breasts into the broth and cook for about 15 minutes, until they are just cooked through and tender.
Using tongs or a slotted spoon, remove the chicken from the broth and transfer it to a plate. Let it rest for a few minutes, then shred it with two forks until it's nicely pulled apart.
While the chicken cools slightly, add the cooked noodles to the pot of broth and stir to combine, allowing the flavors to meld for a couple of minutes.
Return the shredded chicken to the pot, then stir in soy sauce and a squeeze of fresh lemon juice. Taste the broth and season with salt and pepper as needed. Let everything heat through for another 3-5 minutes.
Once the soup is hot and the flavors are balanced, ladle it into bowls, ensuring each has a good mix of vegetables, chicken, and noodles. Serve immediately while steaming hot.
