Place the oil in a large pot over medium heat.
Add the onion, red bell pepper, tomato, garlic, cumin, salt and achiote. Cook, stirring for about 5 to 7 minutes.
Add the broth and bring to a boil. Add the lentils, carrots and plantain, reduce the heat to medium low, cover partially and cook until the lentils are soft about 40 minutes.
Remove from the heat and add the chopped cilantro and serve with white rice and avocado.