Place cucumbers on a cutting board. Using a rolling pin or heavy pan, smash each cucumber firmly until it cracks open and flattens slightly.

Cut smashed cucumbers into 1-inch pieces and place in a colander set over a bowl. Sprinkle with salt and toss to coat. Let drain for 10 minutes.

While cucumbers drain, make the dressing: In a medium bowl, whisk together minced garlic, rice vinegar, soy sauce, sesame oil, sugar, and red pepper flakes (if using).

Rinse cucumbers briefly under cold water to remove excess salt. Pat dry with paper towels or a clean kitchen towel.

Add cucumbers to the dressing bowl and toss until evenly coated. Let marinate for at least 10 minutes at room temperature.

Transfer to a serving dish, sprinkle with toasted sesame seeds, and serve immediately or refrigerate until ready to serve.