Preheat oven to 350F. In large mixing bowl, prepare dressing by whisking together vinegar, apricot nectar, mint, salt and mustard. Core pears and cut into half lengthwise. Cut halves crosswise into thin slices. Add pears to dressing. Stir well. Cover and refrigerate until well chilled.
Spread walnuts on ungreased baking sheet. Toast in 350F oven for 8 to 10 minutes, or until crisp. Set aside.
Wash and dry salad greens. Tear into bite-size pieces and toss with pear and vinaigrette mixture. Divide among 6 salad plates. Top with chopped walnuts.