Trim the beans then cut them into 2 ” lengths. Blanch in boiling water , boiling rapidly for 3-4 minutes. Drain and refresh under cold running water then set aside.
Heat the oil in a large frying pan over a medium heat. When hot add the mustard seeds and , when they start to pop, add the garlic. Stir and fry until lightly browned.
Add the crushed red chilli and stir for a few seconds before adding the beans, salt and sugar. Stir together.
Reduce heat to medium low and cook the beans, stirring, for 7-8 minutes, until they have absorbed the flavour of the spices. Season with black pepper, stir again and serve.