Place cucumbers on a cutting board. Using the flat side of a knife or a heavy pan, smash firmly along the length until the skin splits and the flesh cracks open.
Cut into rough 1.5-inch chunks. Irregular shapes are the point as they grip the dressing better than clean cuts.
Dressing
Mix cucumbers together with fish sauce, lime juice, sugar, garlic, sesame oil, cilantro, and chili flakes. Taste and adjust lime or fish sauce to preference.