Season both sides of the fillets with salt and pepper. Combine cumin, turmeric, saffron and cayenne and sprinkle evenly over fillets. Squeeze cut lime over fillets and drizzle with a little olive oil. Marinate for 15 minutes.
Preheat grill. Rinse plank and place on cooking grate. Cover grill and heat plank for 4 - 5 minutes, or until it starts to throw off a bit of smoke and crackles lightly. Reduce heat to medium low.
Place fillets on plank and cook 15 - 20 minutes. Remove from grill and tent lightly with foil. Let rest for 2 - 3 minutes.
Salsa: In a bowl, gently toss salsa ingredients. Taste and season with salt and pepper.
Serve fillets topped with a dollop of salsa and serve remaining salsa on the side.