In a medium saucepan, bring the salt, vinegar, sugar, celery seed and vegetable oil to a boil, then remove the pan from the heat and allow to cool.
In a large bowl, toss the sliced cucumbers, onions and peppers with the liquid mixture and refrigerate for at least 2 hours and up to overnight. Serve cold.
Before slicing the cucumbers, score the skins vertically with a fork, but do not peel them. Try Kirby or Persian cucumbers if you can find them at your local grocery store or farmers market. They are smaller than regular cucumbers, and are very crunchy and mild in flavor. Perfect for salads!