In a large pot or Dutch oven, heat 1 tablespoon of olive oil over medium heat. Add the chopped onion, carrots, and celery and cook, stirring occasionally, until the vegetables have softened, about 7-8 minutes.
Carefully pour in 8 cups of low-sodium chicken broth and add the 1 1/2 pounds of chicken breasts, 1 teaspoon kosher salt, 1/2 teaspoon black pepper, 1 tablespoon fresh thyme, and 2 bay leaves to the pot. Bring the broth to a gentle boil.
Reduce the heat to low, cover the pot, and let the soup simmer gently for 20 minutes, or until the chicken is cooked through and easily shreds with a fork.
Remove the cooked chicken breasts from the pot and place them on a clean cutting board. Use two forks to shred the chicken into bite-sized pieces, then return all the shredded chicken to the pot.
Increase the heat to medium-high and bring the soup back to a boil. Stir in 4 ounces of whole wheat rotini pasta and cook according to package directions, usually 8-10 minutes, until the pasta is al dente.
Remove the pot from the heat and discard the two bay leaves. Stir in the 1/4 cup of chopped fresh parsley. Taste and adjust seasoning with more salt and pepper if desired before serving.
