In a small bowl, toss the onion with the vinegar, ¼ teaspoon salt, and sumac and let stand for 15 minutes.
In a medium bowl, combine the Asian pears and cucumber with the remaining 1 teaspoon salt, the mint, olive oil, and lemon juice.
Add half the onion to the salad and stir to combine.
Spoon the salad into a serving bowl and garnish with the remaining onion.