Bring a large saucepan of water, 1 teaspoon vegetable oil, 1 pinch salt, and 1 pinch sugar to a boil. Add choy sum and cook for 30 seconds. Drain, pressing gently to squeeze out excess water. Place choy sum on a serving dish.
Heat remaining 2 teaspoons oil in a wok or skillet over high heat. Cook and stir garlic until fragrant, about 30 seconds. Add 2 tablespoons water, oyster sauce, Shaoxing wine, soy sauce, 1/4 teaspoon sugar, and monosodium glutamate; bring to a boil.
Mix remaining 1 tablespoon water and cornstarch together in a small bowl. Pour into the wok; cook and stir until sauce thickens, about 1 minute. Pour sauce over the choy sum.