In a 6- to 8-inch frying pan over medium heat, stir hazelnuts often until golden under skins, 5 to 10 minutes. Pour onto a towel and let stand until cool enough to handle. Rub nuts in towel to remove any loose skins. Lift nuts from towel and reserve; discard skins. Coarsely chop nuts.
In a large bowl, whisk vinegar, oil, and mustard to blend. Cut pears lengthwise into quarters and core; cut quarters lengthwise into thin slices. Drop slices into bowl and mix to coat with dressing. Add spinach and mix gently. Sprinkle with cheese and toasted nuts and mix gently. Add salt and pepper to taste.