Simmer the chicken stock with the Parmesan rind over low heat.
Cook millet in 3 cups of chicken broth until soft, about 40 minutes.
Roast carrots, celery, and onion with olive oil at 400°F for 20 minutes.
Combine roasted vegetables, millet, and chicken in the broth. Add greens and simmer for 10 minutes.
Season with salt and pepper before serving.