||Prepare the Nuoc Cham. Set aside.
||In a bowl, combine the shrimp, fish sauce, half of the garlic, 1/4 teaspoon of the sugar and black pepper to taste. Set aside to marinate for 30 minutes.
||In a wok or large skillet, heat 2 tablespoons of the oil over high heat. Add the remaining garlic and fry until fragrant. Add the marinated shrimp and toss with the garlic until the shrimp turn pink, about 1 minute. Remove to a platter.
||Add the remaining 2 tablespoons oil to the wok. When hot, add the onion and stir-fry over medium heat until lightly caramelized. Add the long beans and toss with the onion for 1 minute. Stir in the soy sauce, salt, the remaining 1/2 teaspoon sugar and 1/4 cup of water. Cook over moderately high heat for 5 minutes, or until the beans are crisp-tender. Add the shrimp and scallions to the wok; toss everything together and remove to a serving platter.
||Sprinkle with black pepper. Serve with rice and Nuoc Cham.