Place lemongrass in a pot of water and bring to a boil. Steam the duck legs in a basket over pot of water for 25–30 minutes. Remove from heat and shred meat. Remove lemongrass from water, use water to rehydrate noodles. Remove noodles from water and reserve.
Combine marinade ingredients in a small bowl. Brush each slice of pork belly with marinade and add a slice of scallion and 1 tablespoon of the shredded duck meat and roll tightly. Cook in sauté pan until crispy on the outside about 7 – 10 minutes.
Combine sauce ingredients in a small bowl.
Combine noodles with shredded shallot, garlic, carrot, cucumber, chili pepper, lime juice and bean sprouts. Top with pork belly, more scallions and cilantro. Pour sauce over meat and noodles, and serve.