squeeze slices to briuse lightly, then cover and chill 30 minutes to 1 hour; drain. In bowl, mix cucumber, onion, vinegar, sugar, and 1/2 teaspoon salt. If made ahead, cover and chill up to 4 hours. Coarsely chop eggplant and spoon onto a rimmed platter; top with cucumber and onion mixture. Add salt to taste.