Prepare haddock according to package directions. Wrap tortillas in foil and reserve until the last 5 minutes of the fish cooking time. Add tortillas to the oven.
Meanwhile, in a bowl toss the lettuce with the tomato, corn, black beans, onions and cilantro leaves (if using).
Lay tacos on a clean work surface. Spoon an equal portion of mango salsa and down the centre of each tortilla. Top with a handful of the lettuce mixture. Chop a piece of fish into bite-sized chunks and arrange over the lettuce mixture. Drizzle with chipotle mayo. Fold over tortilla to serve.