Heat a small skillet over medium-high heat, add the cumin seeds, and toast until the seeds are fragrant and begin to turn brown, 30 to 45 seconds, swirling the seeds occasionally so they toast evenly. With a mortar and pestle or a spice grinder, grind to a coarse powder. Transfer to a large bowl and add the cucumbers and chiles.
Stack the mint leaves, roll them into a tight cylinder, and cut into thin strips. Add to the bowl along with the salt, pepper, and lime juice. Stir gently to combine. Taste and adjust the seasoning, if necessary. Cover the bowl with plastic wrap and refrigerate for 5 to 10 minutes before serving. This salad is best eaten the day it is made.