Heat the oils, soy sauce, and sugar slowly in a wide skillet. Add the green beans and stir to coat with the oil mixture. Cover and cook over medium heat for 5 minutes.
Uncover and raise the heat to medium-high, then stir-fry until the green beans are done to your liking and slightly seared in spots. If needed, add small amounts of water, just enough to keep the skillet slightly moist, but not so much as to prevent the beans from browning. Cooking time will vary according to the tenderness and thickness of the green beans.
Add the sesame seeds and toss the green beans with the sesame seeds. Serve warm or at room temperature.