Wash the lettuce, if necessary. Peel the onion or scallions. Shred the lettuce; cut the cucumbers (peeled or unpeeled, as you wish) into small dice. Dice the tomatoes (remove the seeds and juice first), and chop the onions finely, using a sharp knife, or an Italian mezzaluna chopper if you have one. Put the prepared vegetables into a salad bowl and mix lightly with the radishes and herbs.

Mix the dressing ingredients thoroughly, sprinkle over the salad, and toss well.