Heat 1 tablespoon butter in a large stockpot over medium heat.
Season chicken with salt and pepper.
Add chicken to the stockpot and cook until golden, about 2-3 minutes; set aside.
Add remaining 1 tablespoon butter to the stockpot.
Add garlic, onion, carrots and celery.
Cook, stirring occasionally, until tender, about 3-4 minutes.
Stir in thyme and rosemary until fragrant, about 1 minute.
Whisk in chicken stock, bay leaf and 2 cups water; bring to a boil.
Stir in zucchini noodles and chicken; reduce heat and simmer until zucchini is tender, about 3-5 minutes.
Stir in lemon juice; season with salt and pepper, to taste.
Serve immediately, garnished with rosemary