In a large pot, heat olive oil over medium heat. Add onion, carrots, celery, and garlic; season with salt and pepper. Cook, stirring occasionally, until the vegetables begin to soften (about 3-5 minutes).
Add chicken broth, water, bay leaf, and thyme. Bring to a boil; reduce heat to low, cover, and simmer until vegetables are tender (about 10 minutes).
Stir in cooked chicken and dry pasta. Simmer, uncovered, until the pasta is tender (about 8-10 minutes). Stir regularly so that the pasta doesn’t stick.
Remove bay leaf. Season soup with salt and pepper, to taste. Stir in extra chicken broth to thin, as necessary.
Ladle soup into bowls and garnish with fresh lemon juice and chopped fresh herbs, if desired.