In a large bowl, combine flour, granulated sugar, baking soda, baking powder and salt. Make a well in the center of flour mixture.
In medium bowl, combine egg, buttermilk, orange juice concentrate and melted butter; add all at once to flour mixture. Stir just until moistened (batter should be lumpy). Fold in walnuts.
Line twelve 2-1/2-inch muffin cups with paper bake cups. Fill the cups 3/4 full with batter. Bake in a 400 degree F. oven for 18 to 20 minutes or until muffins are golden. Remove the muffins from the pans.
In a small bowl, combine powdered sugar, orange peel and enough orange juice (2 to 3 teaspoons) to make a drizzling consistency. Drizzle over warm muffins.