Marinate beef with marinade for several hours or preferably overnight. Toss marinated beef in corn flour and shallow fry in hot oil over high heat.
When the beef strips are just tender and browned, remove from the saucepan and leave aside.
Heat a wok with one to two tablespoons oil and fry ginger and garlic until fragrant. Add in sauce ingredients and bring to a boil. Stir in the capsicum and spring onion. Add the beef strips and toss briefly to mix. Remove and serve immediately.