Whisk 1 teaspoon dijon mustard, ½ teaspoon kosher salt, 2 tablespoons white wine vinegar, 1 tablespoon hazelnut oil and 3 tablespoons olive oil in a large bowl. Add 1 pint halved cherry tomatoes, 3 chopped endives and 4 chopped cucumbers; season with salt and pepper and toss. Top with chopped toasted hazelnuts.