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.