Grate the unpeeled cucumber using the large holes of a cheese grater. Measure ½ cup and place it in a bowl lined with paper towels or a kitchen towel. Squeeze out as much liquid as possible to keep the sauce from getting watery.
Transfer the drained cucumber to a medium bowl. Zest the lemon to get ½ teaspoon, then juice it to get 1 tablespoon. Add both to the bowl along with the Greek yogurt, garlic, olive oil, red wine vinegar, salt, and pepper.
