Wash the fish well and dry with paper towels. Lay it skin side down in a single layer in a large dish and sprinkle with salt and lemon juice. Set aside for 15 minutes. Line a fine mesh sieve with a double layer of cheesecloth or a coffee filter, set over a bowl, and pour in the yogurt. Let it drain for 15 minutes or longer.
Scrape the yogurt into a small bowl. Add the grated garlic, ginger, black pepper, ground coriander, ground cumin, garam masala, saffron (if using), dried fenugreek leaves, and butter. Mix well. In a clean coffee or spice grinder, powder the almonds, cashews, coconut, pistachios, and fennel seeds. Mix into the spiced yogurt.
Drain the liquid accumulated at the bottom of the fillets, then smear the spiced yogurt marinade all over the fleshy side of the fish. Cover and marinate in the refrigerator for at least 2 hours. Just before grilling, sprinkle the breadcrumbs all over the fish and pat gently to hold in place.
When ready to grill, place the fish skin side down in a covered barbecue over medium heat. Grill until the bottom is well cooked, about 10 minutes. Flip carefully and cook for another 10 minutes or until it is cooked through. Remove to a platter and sprinkle with lemon juice. Split the fillet down the center and serve.
Recipe courtesy of CUISINES OF INDIA (Ecco Press, 2001) by Smita Chandra and Sanjeev Chandra