Dice the chicken breasts, chop the onion, carrots, celery, and garlic. Rinse the rice.
Heat olive oil in a large pot over medium heat. Add the chopped onion, carrots, celery, and garlic, sautéing for about 5 minutes until softened.
Add diced chicken to the pot, cooking until browned and fully cooked through, about 5-7 minutes.
Pour in chicken broth, water, bay leaf, and dried thyme. Stir to combine and bring to a simmer.
Stir in the rice and season with salt and pepper to taste. Let the soup simmer for 20-25 minutes until the rice is cooked and the chicken is tender.
Remove the bay leaf, taste for seasoning adjustments, and serve hot. Optionally, garnish with fresh parsley.