Slice pork into ¼ inch thick pieces, 3 to 4 inches wide. Place in a nonreactive bowl (glass or ceramic).
In a food processor blend all the marinade ingredients until smooth. The lemongrass fibers will still show but there should be no big chunks. Pour over the pork slices. Each piece should be coated with the mixture. Refrigerate overnight.
Preheat grill to medium-high heat. Grill 4 minutes per side, or until cooked through.
Allow meat to rest for 10 minutes before serving. Top with cilantro and scallions, serve with lime wedges, and Nuoc Cham dipping sauce.
Combine sugar, fish sauce, and warm water in a small bowl. Stir until sugar dissolves. Stir in garlic, carrots, and serrano chili to taste.
