Place the cucumbers in a resealable plastic bag. Press out as much air as possible. Using a rolling pin or a cast-iron skillet, smash the cucumbers.
Add the soy sauce, oil, vinegar, and red pepper flakes to the bag, season with salt, and massage the ingredients to combine. Taste and adjust the seasoning as necessary.
Transfer the seasoned cucumbers to a serving plate, garnish with the sesame seeds and Rayu, and serve immediately.
