firm white fish fillets (e.g., cod, tilapia, or haddock), cut into large chunks • large onion, finely chopped • garlic cloves, minced • -inch piece of ginger, grated • green chilies, chopped (optional, for heat) • coconut milk • water or fish stock • Vegetable oil • mustard seeds (optional) • turmeric powder • curry powder (or fish curry masala, if available) • ground coriander •