Wash the sukuma wiki under cold running water. Cut it into very fine strips.
Heat the oil in a frying pan. Add the onion and cook till light brown. Add the tomatoes and cook till it forms a paste. Then add the sukuma wiki and fry until wilted, about 4 to 5 minutes. Season with salt and pepper and stir for few seconds. Remove remove from the heat and serve.
Serve the sukuma wiki with Ugali, a polenta-like dish, or other starches.