For the Mustard Vinaigrette: In a small bowl whisk together all ingredients. Taste and adjust seasonings with salt and pepper.
For the Tricolored Vegetable Salad: Place vegetables in three separate small bowl bowls. Pour 1/3 of the dressing over each vegetable. Toss to combine. Season, to taste, with salt and pepper if needed. Let stand for at least 1 hour or up to 4 hours. Serve on platter in separate mounds.
Recipe courtesy of Kathleen Daelemans