PLACE grape tomatoes, bocconcini, proscuitto, olives and capers in large bowl.
WHISK together white wine vinegar, mustard, black pepper and sugar in small bowl. Slowly add olive oil in a steady stream, whisking while pouring. Whisk until dressing is well blended. Whisk in chives and oregano. Pour dressing over salad. Gently toss to combine.
REFRIGERATE, covered, several hours or overnight to allow flavors to develop, stirring occasionally. Season with additional black pepper if desired.
TRANSFER tomato mixture to a serving bowl using a slotted spoon. Garnish with fresh oregano sprigs, if desired. Serve.
Using a mixture of red and yellow grape tomatoes adds variety and interest.