Heat oven to 200C/180C fan/gas 6. Slice the cod into 2cm chunks and toss with the chipotle paste, lime juice and olive oil. Leave to marinate while you make the slaw. Mix all the slaw ingredients together, season and set aside.
Put the cod on a baking tray and roast for 10-12 mins until flaking apart. About 4 mins before the cooking time is up, put the taco shells on a separate tray in the oven to warm through.
Serve the tacos filled with the cod and a spoonful of the slaw. Serve the extra slaw on the side.