Slice cucumbers in half lengthwise and scoop out the seeds. Thinly slice into half moons.
Combine vinegar, sugar and salt in a large bowl and stir to dissolve. Add the cucumber slices and stir well to combine.
Toast the rice in a small skillet over medium heat, tossing constantly to prevent burning. Allow it to come to a golden color, similar to brown rice. Using a mortar and pestle or a coffee grinder, process the rice grains to a coarse powder.
Sprinkle the salad with the toasted rice powder and serve immediately.