Rinse fillets and pat dry with paper towels. In a medium bowl mix together the soy sauce, mirin, sugar, garlic and fresh ginger. Place fillets into the marinade and let stand for at least 20 minutes – or preferably 4 hours or longer.
In a salad bowl, mix the chick peas, bean sprouts, water chestnuts, carrot, cucumber, coriander and mint.
Separately, combine the lemongrass, lime juice and extra garlic, and after basting the fish, add the remaining marinade.
Grill or BBQ the fish until cooked through, 5 - 6 minutes on each side depending on thickness, basting occasionally with the marinade.
When the fish is cooked through, add the remaining marinade to the lemongrass mix, and mix thoroughly into the salad. Serve while the fish is hot.