Preheat oven to 400 degrees. Pour 2 tablespoons of the olive oil over the shallots and place in a baking dish. Bake until charred, about 20 minutes. Remove from oven and set aside. Whisk the balsamic vinegar with the Dijon mustard. Gradually add the remaining olive oil and whisk until creamy. Salt to taste and set aside. In a medium salad bowl, combine the roasted shallots, tomatoes, and the arugula. Toss with the oil and vinegar mixture until well coated. Sprinkle with peppercorn mix and toss. Divide the salad on 4 individual salad plates and serve at room temperature. Serves 4.