Cut the sashimi-grade cod into small, equal cubes. Place the fish in a bowl and pour the juice of the two limes over it. Add a pinch of Celtic sea salt and stir well. Let the fish sit for ten to fifteen minutes, so the acid has time to cure the cod.
Meanwhile, finely mince the red onion half. Remove the seed membranes from the red bell pepper half and cut the flesh into small pieces. Peel the mango half and avocado half and cut both into cubes roughly the same size as the fish pieces.
Add the prepared red onion, red bell pepper, mango and avocado to the bowl with the marinated cod and its liquid. Gently stir everything together to prevent the delicate fish and avocado from breaking apart, but make sure all the flavors combine well.
Distribute a generous handful of mixed greens on a plate or bowl. Spoon the fish and fruit mixture onto the greens and, if desired, drizzle with a little more of the remaining lime juice from the bowl. Roughly chop the fresh cilantro and sprinkle it over the dish immediately.