Vinegar Cucumber Salad is a classic side dish made with vinegar (usually apple cider vinegar), water, onions, salt and pepper.
Use your favorite type of onion. The recipe linked uses a sweet onion, but you can use red onions if desired.
3 or 4 large cucumbers 1/2 large sweet onion 1.5 C vinegar 2.5 C water salt & pepper to taste
Click below for the full recipe.
Some people like to add 2 or 3 tablespoons of sugar for added sweetness.