In a medium bowl, combine the rice wine vinegar, water, sugar and salt. Stir together until sugar has disolved then add the thinly sliced carrots and daikon. Set aside.
Slice the pork tenderloin into 1/2 inch medallions and place each medallion between two sheets of plastic wrap. With a rolling pin or heavy bottomed skillet, flatten each medallion to 1/4 inch thickness. In a small bowl mix together the remaining pork ingredients then add the pork. Allow to marinade for at least 30 minutes or overnight.
While the pork is marinating, prep the remaining Banh Mi ingredients. Slice the cucumbers into matchsticks, finely slice the jalapeno into rounds, and pull 1/4 cup of fresh cilantro leaves from their stems.
Heat your grill or griddle pan to medium-high heat. Grill the pork medallions for 2-3 minutes on each side, careful not to over cook. Once each piece is off the grill, cover the pork with aluminum foil and allow the pork to rest for 5-10 minutes.
Slice the bagguettes and dress each side with 1 Tbsp of mayonaisse. Layer each sandwich with cucumbers, pork, pickled veggies, jalapenos and cilantro. Serve while pork is still warm.