How to Make It
Bring a medium saucepan of water to a boil. Add noodles; cook 3 minutes. Drain; rinse under cold water. Drain.
Place onion in a bowl of ice water; let stand 10 minutes. Drain. Combine 2 tablespoons juice, 1 tablespoon fish sauce, garlic, 1 1/2 tablespoons sugar, and black pepper. Add pork; toss.
Combine remaining 1 1/2 tablespoons sugar and 1/4 cup hot water, stirring until sugar dissolves. Add remaining 3 tablespoons juice, remaining 1 tablespoon fish sauce, and crushed red pepper. Add noodles, onion, spinach, carrot, and cilantro; toss.
Heat a wok or large skillet over high heat. Add oil; swirl. Add pork mixture; stir-fry 4 minutes. Divide spinach mixture among 6 plates; top evenly with pork.