Preheat oven to 350 degrees. Line 16 cups of
two 12-cup muffin tins with baking cups,
and lightly coat each with cooking spray.
Whisk together sugar, flours, baking soda,
and 1/4 teaspoon salt in a large bowl. Whisk
together milk, yogurt, eggs, and orange zest
and juice in a medium bowl. Fold milk
mixture into flour mixture, then gently fold
in pears until combined.
Spoon batter into baking cups until each
is three-quarters full. Sprinkle with hazelnuts.
Bake until a toothpick inserted into the
center of each comes out clean, about 20 minutes.
Transfer pans to wire racks, and let
cool for 10 minutes. Turn out muffins onto
racks, and let cool completely.