In a small bowl, whisk the oyster sauce, sugar and 3 tbsp. water until the sugar dissolves.
Divide the oil between 2 large skillets; heat over high. Reduce the heat to medium-high, divide the garlic between the skillets and cook, stirring, until fragrant, about 1 minute.
Divide the beans between the skillets; add 2 pinches of salt to each. Stir-fry until the beans are bright green, about 1 minute. Divide the oyster sauce mixture between the skillets. Stir-fry until the beans are just tender and the liquid is absorbed, 5 to 6 minutes.