Step 1In a bowl, combine the broth, sugar and salt.
Step 2Heat a 14-inch flat-bottomed wok over high heat until a bead of water vaporizes within 1 to 2 seconds of contact. Swirl in 2 tablespoons of the oil and add half the beans. Reduce the heat to medium and pan-fry, turning the beans with a metal spatula or tongs, until they have brown spots and begin to wrinkle, 3 to 4 minutes. Transfer to a plate with a slotted spoon. Pan-fry the remaining beans with 1 tablespoon of the oil in the same manner and add to the plate.
Step 3If the unwashed wok is dry, swirl in the remaining 1 tablespoon of oil over medium heat. Add the ginger and ground pork and stir-fry until the pork is no longer pink, breaking it up with a spatula, about 2 minutes.
Step 4Stir the broth mixture and swirl it into the wok. Bring to a boil over high heat and add the beans, tossing to combine, and cook until most of the liquid has evaporated, 1 to 2 minutes. Add the vinegar, sesame oil and scallion and remove from the heat. Place on a serving platter. Serve at room temperature.