Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the sweet potatoes and slice them into chips about as large as your index finger. Tip them into a bowl. Add 1 tbsp olive oil and some salt and pepper. Toss a few times to coat in the seasoned oil.
Spread the chips out on a baking tray. Slide onto the top shelf of the oven and bake for 20 mins.
While the chips cook, peel and finely chop the onion. Tip into a bowl. Finely grate in the lime zest and squeeze in the juice from one half. Halve the avocado. Scoop out the stone with a spoon. Scoop the flesh out of the skins. Finely chop it. Add to the bowl and toss to coat in the lime juice.
Add a pinch or two of cayenne to the salsa (it’s spicy, so use as little or as much as you like). Season with salt and pepper. Stir a few times to mix. Set aside.
Line a baking tray with baking paper. Sprinkle 2 tsp Cajun seasoning on a plate and stir in the breadcrumbs. Sprinkle 1 tbsp flour onto a separate plate. Crack the egg onto a third plate and beat it to break it up.
Dip the cod fillets in the flour, then the egg and then the breadcrumbs to coat them completely. Pop them on the baking tray.
The chips should have been cooking for 20 mins by now. Turn them over and return to the oven on the middle shelf. Slide the cod onto the top shelf of the oven. Bake for another 10-12 mins. The chips should be tender and the fish white and opaque. It will flake easily when pressed with a fork.
Serve the cod with the chips, avocado salsa, salad leaves and wedges of the remaining lime for squeezing.