1. Heat walnuts in a small skillet over medium-high heat, stirring constantly, 5 minutes or until toasted and fragrant.
2. Whisk together balsamic vinegar, next 2 ingredients, and salt and freshly ground pepper to taste in a small bowl. Combine walnuts, spinach mix, and next 3 ingredients in a large bowl. Drizzle with desired amount of vinaigrette, and toss to combine. Serve immediately with remaining vinaigrette.