In a large bowl, combine flour, pecans, sugar and baking powder.
Combine egg, yogurt, butter and vanilla; mix well.
Stir into dry ingredients just until moistened.
Fold in peaches.
Fill greased or paper-lined muffin cups two-thirds full.
Bake at 400° for 15-20 minutes or until muffins test done.
Cool in pan 10 minutes before removing to a wire rack.