Cut ends off green beans and slice in half. Boil in water with salt for 3 minutes. Drain and rinse with cold water.
In wok with oil, fry garlic, ginger, onions, serrano pepper until color changes (3 minutes)
Add beans and continue stirring.
Add oyster sauce, wine, sugar and sesame oil. Continue frying for about 5 minutes.
Mix corn starch with water and add to wok. Stir until sauce thickens.