Orange beef with green peppers
Diagonally cut the beef, against the grain, into slices 1cm/1⁄2in thick.
In a bowl, combine the orange juice, soy sauce, peanut butter, orange zest, garlic, curry, vinegar and red pepper flakes. Stir to blend. Add the beef and toss to coat evenly. Cover and set aside to marinate for 2 hours at room temperature.
Heat the oil in a heavy frying pan or wok over a high heat. Add the marinated beef mixture. Stir-fry for 2 minutes. Remove the beef with a slotted spoon and set aside on a plate.
Add the green peppers to the pan, then stir-fry for about 5 minutes until the peppers are browned around the edges.
Return the beef to the pan, and stir-fry for a further 1 minute to heat through. Serve hot.