Preheat the oven to gas 7, 220°C, fan 200°C.
Put the sliced peppers and whole chillies on a baking tray. Add the olive oil, season and toss together. Roast in the oven for 30 mins, or until softened.
Meanwhile, put the onion in a bowl with the lime juice and a pinch of salt. Mix well and leave to soften for 20 mins, tossing halfway through.
Empty the spice mix from the taco kit into a dish. Turn each cod loin in the seasoning until completely coated.
Take the tray out of the oven and remove the chillies. Spread out the peppers, nestle the cod among them and return to the oven for a further 12–15 mins, until the cod is cooked through and the peppers are charred at the edges.
Meanwhile, remove the seeds and any charred skin from the chillies. Finely chop the flesh and stir into the salsa from the taco kit.
To serve, flake the fish into a bowl and serve alongside the peppers, onions, coriander, lettuce, salsa, lime wedges and taco shells so everyone can assemble their own and tuck in.
