Combine rice vinegar, sugar, salt, and 1/2 cup warm water. Add shredded carrot and daikon, stir, and set aside for at least 30 minutes.
Mix soy sauce, fish sauce, sugar, garlic, shallot, and lemongrass. Add pork and marinate 30 minutes or overnight.
Grill or pan-fry pork slices until caramelized and cooked through.
Toast baguettes lightly for crisp texture.
Slice open baguettes. Spread mayo and optional pâté. Layer with cooked pork, pickled vegetables, cucumber, jalapeño, and cilantro.
Serve warm with extra pickles on the side.