In a bowl, stir together the sugar, salt, pepper, fish sauce, and lime juice. If needed, tweak the flavor to get a slightly tart-sweet, salty finish. Add the oil, then the chicken, coating the pieces well. Cover with plastic wrap and marinate at room temperature for 30 minutes.
Place the carrot and daikons in a bowl and sprinkle with the salt and 2 teaspoons of the sugar. Use your hands to knead the vegetables for about 3 minutes, expelling the water from them. They will soften and liquid will pool at the bottom of the bowl. Stop kneading when you can bend a piece of daikon so that the ends touch but the daikon does not break. The vegetables should have lost about one-fourth of their volume. Drain in a colander and rinse under cold running water, then press gently to expel extra water. Return the vegetables to the bowl if you plan to eat them soon, or transfer them to a 1-quart jar for longer storage.
Cut baguettes into six 6-inch pieces. Slice the rolls in half, but not all the way through so one side of top and bottom remain attached. If the bread is soft, crisp it slightly in a toaster.
Spread 1 to 2 teaspoons of mayonnaise on each roll. Pile the chicken into the rolls, followed by a small pile of the Daikon Carrot Pickle (you will not use up all the pickle), cucumber slices, optional jalapeno slices, and a few sprigs of fresh cilantro.