Apple Streusel Muffins *

1 pkg (6 1/2 oz) apple cinnamon muffin mix
1 large tart apple, peeled and diced
1/3 cup chopped walnuts
3 Tbsp brown sugar
4 1/2 tsp all purpose flour
1 Tbsp butter, melted

Glaze: 
3/4 cup powdered sugar
1/2 tsp vanilla
1-2 Tbsp milk

Prepare muffin mix as directed on package; fold in apple.  Fill greased muffin cups.  In a bowl, combine walnuts, brown sugar, flour, and butter. Sprinkle over batter.  Bake at 400 for 15-20 minutes.  In another bowl, combine glaze ingredients.  Drizzle over warm muffins.