Chop the beef into cubes, seed and dice the capsicums. Peel the onion and dice. Lightly beat the egg.
Preheat the wok, add the oil, and heat. Add egg and fry until solid, then transfer to the plate. Add beef, onion, capsicums, and stir fry. Add salt and soy sauce, and stir well. Add fried egg and cold rice, stir fry. When the rice becomes hot, it is ready to serve.