Whisk together the vinegar, zest, lemon juice, mustard, salt and pepper in a medium mixing bowl. While whisking constantly, gradually add the olive oil. Add the broccoli and toss to coat. Cover and place in the refrigerator for 1 hour.
Stir in the tomatoes, hazelnuts and basil. Cover and allow to sit, at room temperature or in the refrigerator, for another 15 minutes before serving.
Recipe courtesy of Alton Brown, 2007