Place the shallots in a small shallow bowl and pour the vinegar over them. Set aside for 10 minutes to macerate.
In a large shallow serving bowl, combine the radicchio, endive, arugula, oranges, and olives. Lift the shallots from the vinegar with a slotted spoon, sprinkle them on the salad, and toss lightly (discard the vinegar).
In a 1-cup glass measuring cup, whisk together the lemon juice, mustard, 1 teaspoon salt, and 1/2 teaspoon pepper. While whisking, slowly add the olive oil. Pour enough of the vinaigrette over the salad to moisten well. Sprinkle with one more teaspoon salt, toss well, and taste for seasonings. Serve at room temperature.