In a small bowl, whisk together the Balsomic Vinegar, Mustard and Shallot. Add Olive Oil in a slow stream whisking until emuslified. Season with Salt & Pepper to taste.
Peel and slice the Mangoes in long thin wedges. Slice the Tomatoes and arrange in an overlapping cirlcle on a decorative platter. Fan the Mango slices on top of Tomatoes with tips converging in the center of the Tomato circle. Place a Basil sprig in the center. Dress with the Vinaigrette and garnish with Basil and Chives. Serve at once.