Heat oil in a medium skillet over medium-high. Add garlic and ginger; cook until fragrant and golden, about 30 seconds. Add bok choy, stirring to evenly coat. Add soy sauce and 2 tablespoons water; cover and cook 2 minutes. Remove lid and continue cooking, stirring a few times, until liquid has evaporated and bok choy is tender, about 2 minutes. Season with more soy sauce, if desired, and serve.