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.