Clean the beans, cut large pods in half, use young or tender beans whole. Mash the garlic and finely chop it.
Blanch the beans in a saucepan with lightly salted, boiling water, drain and rinse under cold water to keep the bright green color.
Heat the oil in a wok or pan until it smokes. Add garlic to flavor the oil. Just before the garlic turns dark brown, add the beans and cook for about 1 minute while stirring. Add salt, sugar and soy sauce and cook for a further 1 minute at most. Serve hot or cold.