In small bowl, combine vinegar, sugar and salt. Add carrots; set aside to pickle, tossing every 5 minutes or so.

Meanwhile, in another small bowl, stir together mayonnaise, fish sauce, sriracha and 2 teaspoons carrot pickling liquid. Set aside.

Bring medium saucepan of water to boil. Cook shrimp until opaque pink-white and a safe internal temperature of 145°F, about 3 minutes. Drain. Place in ice water until cool. Pat dry; set aside.

Divide rice noodles or rice between 4 bowls. Top with pickled carrots, shrimp, cucumber and cilantro; drizzle with sauce. Refrigerate any leftovers.