Asopao de Gandules (Pigeon Pea Stew)

Heat oil in a large pot over medium heat. Add gandules, onion, ají dulce (or bell pepper) and garlic. Cook, stirring occasionally, until the vegetables are soft, about 3 minutes. Add 1 cup broth, tomato paste and oregano. Cook, stirring occasionally, until the liquid is almost completely evaporated, about 5 minutes. Stir in the remaining 3 cups broth, salt and pepper. Reduce heat to maintain a simmer, cover and cook, stirring occasionally, until the vegetables are very tender, about 15 minutes more. Stir in culantro (or cilantro).