Place beef strips in a bowl and add lime rind and juice, fish sauce, soy and sugar.
Cover and marinate for 30-60 minutes in the fridge.
Heat oil in a large wok or frying pan, add onion and garlic and lightly cook.
Add meat and the marinade juices, and brown meat over a high heat, this should take about 2-3 minutes.
Add a pinch of sugar and allow the juices to bubble to reduce slightly.
Add green beans and spring onions, toss well together.
Finish by adding coriander leaves and peanuts.
Serve on a bed of crispy fried rice noodles or steamed rice.