Combine the water, rice vinegar, sugar, and salt and stir until the sugar dissolves.
Add the daikon, carrots, and cucumbers to a large mason jar. Pour the pickling liquid over veggies, screw on the lid, and allow the vegetables to pickle in the refrigerator for at least one hour and up to 24 hours in advance.
Combine the ginger, shallots, garlic, sugar, fish sauce, soy sauce in a medium bowl.
Add the chicken, cover, and allow to marinate for at least 20 minutes or up to 24 hours.
Cook the chicken on an indoor grill or outdoor grill until cooked through. The time will vary depending on the thickness of the chicken breasts. Allow chicken to cool for 5 minutes before slicing.
Mix Sriracha and Mayonnaise.
Toast the baguettes if desired, spread mayonnaise spread on bread and top with chicken slices, pickled vegetables, cilantro leaves, and jalapeño slices. Serve warm.
