First bring a large pot of salted water to boil. Boil noodles according to package directions. While that’s going on, prepare the dressing.Make the dressing:
Place the garlic and ginger in a blender and pulse to chop them up a bit. Add the remaining ingredients – sesame oil, rice vinegar, tamari, sriracha, sugar, peanut butter, and water, and puree until it’s completely smooth. Add a little extra warm water if needed to thin.
When the noodles are ready, run them under cold water to cool completely.
In a large mixing bowl, toss the noodles with the dressing to coat. To assemble, place a bunch of noodles down the center of a romaine heart, leaving a little bit of space at the top and bottom. Sprinkle with black sesame seeds. Tie each heart up with a whole scallion to form a bundle.