In a large pot, heat the olive oil over medium heat.
Add the chopped onion and sauté until translucent.
Stir in the minced garlic, cooking for another minute.
Add the diced carrots and celery, sautéing for 5 minutes.
Pour in the chicken broth and bring to a boil.
Add the chicken breasts to the pot and reduce heat to a simmer.
Cook the chicken for about 20 minutes, or until fully cooked.
Remove the chicken, shred it, and return it to the pot.
Add the lemon slices and chopped parsley, stirring well.
Season with salt and pepper to taste, and serve hot.