Place basa fillets on a baking tray lined with baking paper. Sprinkle with half the lemon zest and season with salt and pepper. Drizzle with olive oil and cook in the oven for 10-12 minutes, until opaque and just cooked through, depending on the thickness of the fillet. Remove from oven and cool.
In a large bowl, combine red onion, coriander, mayonnaise, egg, the remaining lemon zest and juice, paprika and cayenne pepper. Mix until well combined. Break the basa fillet into large flakes and add to the bowl. Add the breadcrumbs and season with salt and pepper. Mix gently until well combined.
Roll the mixture into 8 balls, press into 1½ cm patties and place on a tray lined with baking paper. Cover and chill for at least one hour.
Heat enough oil to come up to 3mm in a large heavy based frying pan over high heat. Working in 2 batches, fry cakes for 4 minutes on each side, or until browned. Drain on paper towels and keep covered with foil while cooking the second batch.
For the salad, gently toss all ingredients in a large bowl and season with salt and pepper. Serve with the fish cakes and drizzle with any remaining dressing
Notes: Prep Time 20 minutes + 1 hour Chilling Time Cook Time 20 minutes