Gather all your ingredients: chicken breasts, vegetables, broth, lemon, and tools like a knife, zester, and large pot.
Heat a tablespoon of olive oil in the large pot over medium heat until it begins to shimmer and smells slightly nutty.
Add diced onion, sliced carrots, and chopped celery to the pot. Sauté for about 5-7 minutes until the vegetables become fragrant, slightly softened, and begin to develop a gentle golden color.
Push the vegetables to the sides of the pot and add the chicken breasts in the center. Cook for 4-5 minutes per side, until they turn opaque and develop a slight sear.
Pour in the chicken broth, scraping the bottom of the pot gently to loosen any flavorful bits. Bring the mixture to a gentle simmer.
Reduce the heat to low and let the soup simmer for about 20 minutes, until the chicken is cooked through and the vegetables are tender.
While the soup simmers, zest the lemon using a zester or microplane, collecting fine strips of lemon peel, and set aside. Also, squeeze half of the lemon to extract fresh juice.
Remove the chicken breasts from the soup and shred them into bite-sized pieces, then return to the pot, stirring gently to distribute.
Add the lemon zest and juice to the soup, stirring well. Taste and adjust the seasoning with more lemon juice if you prefer a brighter flavor.
Cook for an additional 2-3 minutes to let the flavors meld, then turn off the heat.
Serve the soup hot, with fresh lemon zest sprinkled on top for a vibrant finish. Enjoy the bright, comforting flavors in every spoonful!