In a skillet set over moderate heat, warm the oil until it is hot. Add the onion and pepper and cook, stirring, for 5 minutes, or until softened. Add the garlic, gingerroot and curry powder and cook, stirring, for 2 minutes. Add the tuna, chilies and salt and cook, stirring, until heated through. Season with lemon or lime juice and toss with cilantro. Serve with rice or as a filling for flour tortillas.