Preheat oven to 400° F. In a bowl, toss cut Brussels sprouts in a small amount of olive oil until lightly coated. Arrange, cut side down in a shallow glass roasting dish, and place in the oven for 15-20 minutes until slightly roasted and still crunchy.
While the sprouts are roasting, prepare the Dijon Vinaigrette. Mix all Dijon ingredients except for the capers in a small dish with a spoon until sugar is dissolved and a smooth consistency has been reached. Taste, and adjust seasonings as necessary. Stir in capers. Set in the refrigerator.
Once Brussels sprouts are finished roasting, place them in an uncovered bowl and set them in a cold spot (the freezer works well) for 10-30 minutes, until cooled. Stir carrots and scallions into cooled Brussels sprouts, and finally stir in the Dijon vinaigrette until all vegetables are coated.
Serve chilled.
