In a small bowl, combine the apple and sugar; set aside. Combine the flour, baking powder, cinnamon and salt. In another bowl, whisk the egg, milk, oil and vanilla; stir into dry ingredients just until moistened. Fold in the apple mixture, walnuts and raisins.
Coat muffin cups with cooking spray or use paper liners; fill three-fourths full with batter.
Bake at 375° for 18-20 minutes or until a toothpick inserted in the center comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm.