Heat the peanut oil in a wok or skillet with high sides over medium-high heat until almost smoking; add the green beans. Quickly cook and stir the beans in the hot oil until they are bright green and starting to show brown spots, about 2 minutes. Remove the beans to a bowl. Drain all but 2 tablespoons of oil from the pan and return to heat. Cook and stir the ginger and garlic in the oil until they have started to brown, about 2 minutes. Return the green beans to the wok; add the dark soy sauce, sugar, and black pepper. Cook until hot; about 30 more seconds.