Wash the cucumbers under cool running water, peel if desired, and slice thinly, about ⅛ inch thick. Optionally score lightly with a fork to reduce bitterness. Place in a large mixing bowl.

Peel the sweet onion and slice into rings or half-moons. Soak in cold water for 10 minutes if a milder taste is preferred. Add to the bowl with cucumbers.

Toss the sliced cucumbers and onions together until well-combined.

In a separate bowl, mix the mayonnaise, white sugar, and white vinegar until smooth and creamy.

Pour the dressing over the cucumber and onion mixture. Gently fold the ingredients together and season with salt and pepper.

Cover the bowl and refrigerate for at least six hours or overnight.

Before serving, give the salad a gentle stir and serve chilled.