Puree the vinegar, capers, 1 1/2 tablespoons mustard, and shallots(or green onions) until well blended. Pour into a bowl. Add the remaining mustard around the edge of the bowl and fold into the mixture. Add the oil in a stream while stirring constantly until creamy.
Combine all of the ingredients in a large bowl. Move about 1 1/2 cup of the salad mixture into serving bowls. Coat lightly with some dressing and toss to combine. Serve immediately.