One of Puerto Rico’s staple rice dishes, arroz mamposteao is a combination of bean stew, cooked rice and ripe plantains. It's a popular dish for home cooks since it can be put together in an extremely short amount of time and helps you use any leftover white rice you might have from the day before. Its bright reddish-orange color, topped by the green of the cilantro, is picture-perfect.
Heat the oil in a large pot over medium high. Add the onions and garlic and cook, stirring occasionally, until the onions begin to soften, about 1 minute 30 seconds. Add the sofrito, tomato sauce, tomato paste and sazón and cook, stirring occasionally, until the onions are lightly brown, about 2 minutes. Stir in the plantains, then the beans with their liquid and 1/2 cup water. Season to taste with salt and pepper, reduce the heat to medium low and cook, stirring occasionally, until the flavors meld, about 10 minutes.
Reduce the heat to low, add the rice and cook, stirring continuously, until combined and the flavors meld, about 1 minute. Remove from the heat and fold in the cilantro.
Rinsing the rice in cold water before cooking will prevent it from becoming sticky.