Place sugar in a small, heavy saucepan over medium-high heat; cook until sugar dissolves, stirring gently as needed to dissolve sugar evenly (about 1 minute). Continue cooking 1 minute or until golden (do not stir). Remove from heat; carefully stir in nuts to coat evenly. Spread nuts on a baking sheet coated with cooking spray; separate nuts quickly. Sprinkle with 1/4 teaspoon salt. Set aside until cool; break into small pieces.
Combine vinegar and mustard, stirring with a whisk. Gradually add oil, stirring constantly with a whisk.
Combine lettuces; top with pear and candied walnuts. Drizzle dressing evenly over salad; sprinkle with remaining 1/4 teaspoon salt and pepper.
Toss gently to combine.