Heat the oil in a wok over a high heat until the oil starts to shimmer. Add the garlic, chillies, shallots and beef and cook for 2–3 minutes, until the beef begins to colour. Tip in the pepper, sweetcorn and mushrooms and cook for a further 2 minutes.
Stir in the fish sauce, sugar and soy sauce and cook for a few more seconds, then add the cold cooked rice and the spring onions, stir-frying until the rice is steaming hot. Fold in the coriander and serve.