To handle fresh chilies, cover your hands with rubber or plastic gloves; after handling, do not touch your face or eyes. Cut chilies open lengthwise; remove seeds and pith. Chop chilies.
Heat oil in a large skillet. Add onion and garlic; sautè until golden. Stir in chopped chilies, curry powder and gingerroot. Stirring constantly, cook 2 to 3 minutes. Stir in coconut milk and leek. Simmer 10 minutes. Add crabmeat or shrimp, cod and lemon grass, if desired. Cook 10 minutes over low heat, shaking pan occasionally to prevent burning. Add tomatoes; cook 5 minutes longer. Season with lime or lemon juice; add enough water to moisten ingredients, if necessary. Serve with rice or couscous.