Make the dressing: combine the sugar, a pinch of salt, rice vinegar, soy sauce, and sesame oil and stir until the sugar dissolves. Stir in the toasted sesame seeds.
Bring the water to a boil, then add the salt and cooking sake and lower the heat so the water is hot but not at a rolling boil.
Poach the pork slices a few at a time, spreading each one out and swishing gently, until they just turn pale. Only a few seconds each.
Lift the cooked pork into a strainer to drain and cool. Optionally dip briefly in cold water, but don't let it soak. Cool to room temperature or chill.
Spread the shredded lettuce and cucumber over serving plates, arrange the cooled pork on top, and scatter the cherry tomatoes around.
Stir the dressing and spoon it over the pork and vegetables just before serving. Serve immediately.
