- Combine beef with oyster sauce, corn flour and 1 tsp of oil in a bowl.
- Heat a fry pan or wok over high heat. Add remaining 3 tsp oil and stir-fry onion for 1-2 mins. Add beef and stir-fry for 2-3 mins. Add capsicum and continue stir-frying for 3 mins.
- Stir in pineapple and sweet & sour sauce and cook until heated through, for 2-3 mins.