Make the Green Rice: Combine the water and rice in saucepan with a tight-fitting lid. Season the water with salt. Bring to a boil, lower the heat, and simmer, covered, until tender, about 20 minutes. Set the rice aside, covered, for 10 minutes. Fluff the rice with a fork and stir in the chimichurri. Set aside, covered, until ready to use.
Meanwhile, make the Black Beans: Heat the oil in the saucepan over medium-high heat. Add the cumin seeds and cook, stirring, until fragrant, about 30 seconds. Add the bell pepper and onion and cook, stirring, until soft, about 8 minutes. Stir in the black beans and sugar. Bring to boil, lower the heat, and simmer for 5 minutes. Add the vinegar and season with salt and pepper. Set aside, covered, until ready to use.
Make the Salsa: Preheat a grill pan over high heat. Grill the pineapple rings, turning once, until charred, about 2 minutes. Transfer the rings to a cutting board and chop.
In a bowl, combine the pineapple, mango, bell pepper, onion, cilantro, olive oil, ginger, jalapeno, and lime juice. Season with salt and pepper and set aside. (The salsa can be prepared up to 2 days in advance.)
Make the mahi mahi: Arrange the fillets in baking pan, season with salt and pepper, and rub with the zest. Preheat a cast iron skillet over medium heat for 5 minutes. Raise the heat to high and heat the butter and oil. Working in batches, if necessary, sear the halibut fillets, turning once, until well browned and just cooked through, about 3 minutes per side.
Divide the rice and beans among the center of 6 plates, top with the fillets, and spoon some the salsa over each.
In a food processor, pulse the onion until finely chopped but not pureed. Transfer the onion to a bowl. Add the olive oil, parsley, cilantro, oregano leaves, garlic, and lime juice and pulse until finely chopped. Transfer the herb mixture to the bowl of onion and stir to combine. Season the chimichurri with salt and pepper.
Recipe courtesy of Susanna Goihman, Azafran Restaurant, Philadelphia, PA