The shallots and blue cheese give this mesclun salad a festive touch.
Preheat oven to 425 degrees. On a large rimmed baking sheet, toss shallots with 1 tablespoon oil; season with salt and pepper. Roast, tossing occasionally, until browned and tender, 25 to 30 minutes. Let cool slightly; set aside. In a large serving bowl, whisk together remaining 2 tablespoons oil, vinegar, and Dijon; season dressing with salt and pepper.
Just before serving, add greens and shallots to dressing; toss, and top with cheese and hazelnuts.