Step 1Place mustard and cumin seeds in a frying pan over medium heat; cook, stirring, for 30 seconds or until fragrant. Transfer to a mortar and pestle and pound until finely crushed. Add turmeric, onion powder and lime zest, and stir to combine. Sprinkle spice and lime mixture evenly over fish and spray lightly with olive oil.
Step 2Preheat barbecue hotplate or large grill pan to high heat. Grill fish for 2–3 minutes each side, or until just cooked through.
Step 3Meanwhile, place grated carrot, English spinach, coriander leaves, shredded coconut, lime juice and olive oil in a large salad bowl, and toss gently to combine. Serve spiced fish fillets with shredded carrot and coconut salad, warm naan and lime wedges.