Wash the radishes well and trim off leaves and roots. Slice in rounds. Leave slices whole if the radishes are small but cut the rounds into halves or quarters if radishes are larger. Peel the cucumbers. Cut in half vertically and with a teaspoon scoop out the seeds and discard. Dice the flesh. Trim and wash the scallions and slice thin both white and tender green portions. Seed and chop the green pepper, if you use it. Wash and dry the watercress and pull the leaves off the stems; discard the stems. Cut the tomatoes in small chunks.

Cut the peeled garlic clove in half. Place a pinch of coarse salt in the salad bowl and rub the cut sides of the garlic in it, rubbing all over the bottom and sides of the bowl. Add the vegetables and black pepper to taste and toss together lightly but thoroughly. Serve at once, discarding the garlic halves as you come upon them.