Add the broth, cumin, and bouillon granules, and bring to a boil. Taste for salt, reduce heat slightly, and add chicken pieces back into pot, spaced out evenly. Add the whole Serrano pepper to dish, cover and cook at a low simmer for 12 to 15 minutes. Add diced zucchini on top, making sure you do not mix (disturb) rice. Cover and continue cooking until all of the liquid is absorbed. Remove from heat and let stand for 10 minutes.