For dressing, in a screw-top jar combine oil, vinegar, green onion or chives, and pepper. Cover and shake well; chill till needed.
Cut zucchini or cucumbers in half lengthwise. Seed cucumbers, if using. With a vegetable peeler, cut zucchini or cucumber halves into thin, lengthwise strips (about 1/2 to 1 inch wide). Line a serving platter with leaf lettuce and top with sliced tomatoes. Arrange zucchini or cucumber strips among the tomatoes, tucking and folding the strips as desired. Shake dressing and drizzle atop vegetables. Cover; chill at least 30 minutes. Sprinkle with feta cheese before serving.