Place each half-head of lettuce on individual plates cut side down so the lettuce forms a mound on the plate. Arrange the radishes and cucumber slices around each lettuce mound. Place capers, dill, parsley, shallot, vinegar, salt and pepper in a blender. Turn blender on and stream in extra-virgin olive oil. Test seasonings in the dressing. Spoon the dressing evenly over the salads, capping the lettuce.