Remove the stemsfrom the okra and cut into 1-in. slices.
Heat the oil in a frying pan, then add the onion and cook for about 10 minutes. Add the okra, chili powder, turmeric, tomato, and salt, and cook, covered, for about a half hour (until the okra is tender).
Add the garam masala, cardamom, and nutmeg, and continue cooking, stirring frequently, for another couple of minutes. Serve hot.