Slice the cod into 2cm chunks and toss with the chipotle paste, lime juice and ½ tbsp of the oil. Leave to marinate for 15 minutes if you have time.
When ready to cook, heat the rest of the oil in a non-stick frying pan over a medium heat. Add the onion, pepper and a pinch of salt, stirring to coat the vegetables in the oil. When the onions start to brown, after around 5 minutes, turn down the heat.
Add the cod and cook for around 5 minutes until the fish is cooked throughout and flakes apart easily, and the vegetables are tender but still with some crunch.
Warm the tortillas according to the pack instructions.
Assemble the tacos with the vegetables, cod and avocado slices, topped with the coriander.