Chop the onion and mince the garlic, preparing them for sautéing.
Dice the chicken into bite-sized pieces, setting them aside for later.
Heat a large pot over medium heat and add the olive oil, allowing it to warm up until it shimmers.
Sauté the chopped onions and minced garlic in the hot oil, stirring frequently, until they are fragrant and translucent, about 3-4 minutes.
Add the diced chicken to the pot, cooking until lightly browned and cooked through, about 5 minutes.
Pour in the chicken broth and bring the mixture to a gentle simmer, skimming off any foam that rises to the surface.
Add sliced carrots and celery if using, then let the soup simmer gently for 15-20 minutes until vegetables are tender and chicken is very soft.
Taste the soup and season with salt and pepper as needed, then stir in chopped fresh herbs for a burst of brightness.
Use a ladle to serve the hot, clear broth filled with tender chicken and vegetables, garnished with extra herbs if desired.
