Heat the oil in a large pot or Dutch oven over medium flame. Add the onion and garlic and sauté until the onions are translucent, 4 to 5 minutes.
Stir in the tomatoes and simmer for about 5 more minutes.
Add chicken broth and chicken breast; bring to a boil. Reduce heat to low and simmer for 30 minutes.
Add the carrots and potatoes and simmer for another 30 minutes. Add more stock or water if necessary.
Finally add the pumpkin, plantain, corn, oregano, salt and pepper and simmer for another 30 to 45 minutes, or until the meat is tender and the vegetables have begun to break down a bit.
Adjust seasoning to taste and stir in the cilantro.
Serve hot with rice.