Rinse and drain green beans; trim off and discard stem ends. Cut beans into 2- to 3-inch lengths. In a small bowl, mix soy sauce, rice vinegar, sugar, chili flakes, and white pepper.
Set a 10- to 12-inch frying pan over high heat. When pan is hot, add beans and 1/4 cup water. Cover and cook, stirring once, until beans are bright green and slightly crunchy to bite, 3 to 4 minutes. Uncover and cook until any remaining water has evaporated.
Add oil, garlic, and ginger to pan; stir until green beans and garlic are lightly browned, 1 to 2 minutes. Stir soy mixture and add to pan; bring to a boil and stir until most of the liquid has evaporated and the sauce thickens and coats the beans, 2 to 3 minutes. Pour into a serving dish. Serve hot or cool.