Heat walnuts in a small skillet over medium-high heat stirring constantly 5 minutes or so until toasted. Whisk together Blueberry balsamic and the extra virgin olive oil and add fresh ground pepper and salt to taste. Combine walnuts, spring mix, blueberries, onion, and blue cheese in large salad bowl. Drizzle blueberry vinaigrette and toss to coat. Serve immediately.