Cut fish into bite-sized squares. Sprinkle with salt and allow to stand for a minute. Heat 1 tablespoon of the ghee in a heavy frying pan, and fry the fish on both sides until golden. Remove from pan and set aside. Add remaining ghee to pan, and heat. Add ginger, onion, garlic and curry powder and stir until onion is softened, about 3 minutes. Add coconut milk and simmer uncovered until sauce is reduced and thickened. Add fish and simmer for another minute or two, until fish is heated through. Stir in tamarind juice or vinegar and taste for seasoning (more salt may be needed). Serve with rice and a few side dishes if desired (for instance, chopped peanuts, desiccated coconut, chutney, chopped tomato, mint).