Preheat oven to 350 degrees. Line 16 cups oftwo 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. Whisktogether milk, yogurt, eggs, and orange zestand juice in a medium bowl. Fold milkmixture into flour mixture, then gently foldin pears until combined.
Spoon batter into baking cups until eachis three-quarters full. Sprinkle with hazelnuts.Bake until a toothpick inserted into thecenter of each comes out clean, about 20 minutes.Transfer pans to wire racks, and letcool for 10 minutes. Turn out muffins ontoracks, and let cool completely.