Gather all your ingredients and prep your tools, including chopping the onion, carrots, celery, and dicing the chicken.
Heat the large pot over medium heat and add olive oil, letting it warm until shimmering.
Add the chopped onion to the pot and sauté for about 5 minutes until it becomes soft, fragrant, and translucent.
Stir in the diced chicken and cook for about 7 minutes, stirring occasionally until the chicken is browned and cooked through.
Pour in the chicken broth, bring the mixture to a gentle simmer, and cook for 15 minutes, skimming foam off the surface as needed.
Add the sliced carrots and celery to the pot, stirring them into the simmering broth.
Continue simmering for another 10 minutes, until the vegetables are tender and the flavors meld.
Season the soup with salt and pepper to taste, then squeeze in the fresh lemon juice for brightness.
Let the soup rest off heat for a couple of minutes, allowing the flavors to settle and develop.
Taste and adjust seasoning if needed, then sprinkle with chopped parsley or thyme for a fresh herbal note.
Serve the hot, comforting soup in bowls, enjoying the tender chicken and bright, flavorful broth.