Peel the cucumbers and slice them in half lengthwise. Using a spoon, scoop out the seeds. Cut into thin slices and place in a colander. Sprinkle with 2 tsp. salt and toss to combine. Let sit.
In a large bowl, whisk the yogurt, dill, lemon juice, sugar and salt.
Rinse the cucumbers with water and dry thoroughly with paper towels. Add the cucumbers and onions to the yogurt mixture and stir gently to combine. Store in the refrigerator in an airtight container. Serve chilled.