For the marinade, in a bowl, mix together the plain yoghurt, the juice of one lime, the garlic, ginger, cumin, coriander, garam masala, paprika and salt until well combined.
Add the trout fillets and coat them in the marinade mixture. Cover and chill in the fridge overnight, or for at least for two hours.
When the trout has marinated, preheat the grill to its highest setting. In a bowl, mix together the melted butter and the juice of the remaining lime until well combined.
When the grill is hot, place the marinated trout fillets under it and grill for 2-3 minutes. Baste the grilled trout fillets with the lime juice and butter mixture.
Turn the trout fillets over and grill for a further 2-3 minutes, basting with the lime juice and butter mixture halfway through cooking.
For the salad, mix the curry paste with the boiling water until dissolved. In a separate bowl, mix together the onion, mixed beans, lime juice, malt vinegar, olive oil, coriander and chopped red chilli until well combined.
To serve, divide the salad equally among four serving plates. Place one tandoori trout fillet on top of each portion. Serve the naan bread alongside.