Cut the trout fillets into 3-inch pieces. Stir together the yogurt and turmeric, add the trout and toss to coat. Marinate for at least an hour, or preferably overnight.
Heat a large skillet over high heat and add the oil. Dredge the fillets with rice flour and place skin side down in the pan. Cook for about 2 minutes, or until the skin is crispy and golden. Flip the fish over add the butter, garlic, dill and green onions to the pan. Baste the fish in the butter and continue to cook for about a minute. Transfer the fish to a plate and pour the butter and herbs from the pan over the fish.
Prepare the nuoc cham sauce: bring the fish sauce, sugar, water and garlic to a simmer in a small saucepan. Remove from heat and add the chopped chillies and the lime juice. Chill before serving.
Arrange the noodles on a plate and top with the fish fillets, dill and scallions. Serve with shrimp crackers, peanuts and nuoc cham sauce. Serves 4-6.