Toast the cumin seeds for one to two minutes in a dry pan over a medium heat until fragrant, pound in a pestle and mortar into a powder. Roughly chop half the coriander including the stalks. Mix the radishes with the cumin, chopped coriander, juice from ½ a lime and season to taste.
Carefully separate the brown and the white meat, don’t worry if a little brown is mixed in with the white or vice versa.
Heat a griddle pan and toast the tacos until strong lines appear. Blob each taco with the crème fraîche and marble in a ¼ of the brown crab, sprinkle over ¼ of the lime zest and chilli. Top the tacos with the shredded lettuce, mango and radishes, finish each with the white meat and a couple of coriander leaves.
Season with salt and pepper.