For the relish, whisk together the lime juice, oil, honey, salt and pepper in a medium bowl. Add the avocado, mango, red onion and cilantro, and gently mix to combine. The relish can be made 30 minutes in advance.
For the black bean sauce, combine beans, onion, garlic, chipotle and cumin in a medium saucepan and add just enough cold water to cover by an inch. Bring to a boil, reduce heat and simmer until beans are soft.
Transfer mixture to a food processor with a slotted spoon and add 1 cup of the cooking liquid and process until almost smooth; the sauce should be a little chunky. If the sauce is too thick, thin with a little cooking liquid. Season with salt.
For the crema, combine the creme fraiche or sour cream and jalapeno in a food processor and process until smooth. Season with salt and pepper, and refrigerate for at least 30 minutes before serving. This can be made and refrigerated up to 1 day in advance.
Brush the snapper with oil on the skin-side and season with salt and pepper. Cover the surface of the fish with the plantains, overlapping them. Brush the top with oil and season with salt and pepper.
Heat a few tablespoons of oil in a large nonstick pan over medium-high heat and carefully place the fish in the pan, plantain side down. Cook until the crust is lightly golden brown, about 4 minutes. Turn the fish over and continue cooking until just cooked through, about 4 minutes longer.
Spoon some of the black bean sauce onto 4 plates and drizzle with some of the jalapeno crema. Set the snapper, plantain side up, on top. Spoon some mango-avocado relish next to the fish and garnish with chive oil, if desired.