1. Combine brown sugar, soy sauce, and 1 tablespoon fish sauce in a large zip-top plastic storage bag. Add pork, turning to coat; seal and chill 1 hour or overnight.
2. Combine chili-garlic sauce, lime juice, sugar, and remaining 3 tablespoons fish sauce in a medium bowl. Add hot water, stirring until sugar dissolves. Set aside.
3. Cook rice noodles according to package directions; drain. Toss noodles in chili-garlic sauce mixture.
4. Remove pork from marinade, discarding marinade. Heat oil in a large nonstick skillet over medium-high heat. Cook pork, in batches if necessary, 2 minutes on each side or until inside is done and edges are slightly crispy.
5. Combine salad greens, cucumber, and next 4 ingredients on a serving platter. Top with noodle mixture and pork. Garnish, if desired.