1. Place potatoes in a medium saucepan, and cover with cold water. Bring to a boil. Reduce heat, and simmer 10 minutes or until potatoes are tender. Drain.
2. Combine rice vinegar and the next 6 ingredients (through jalapeño) in a large bowl, stirring well with a whisk. Add potatoes to lemongrass mixture; toss gently to combine. Cool completely.
3. Sprinkle potato mixture with green onions and cilantro; toss well to combine.