Heat oven to 375°F. Coat 2 standard muffin pans (12 cups each) with cooking spray.
Mix flour, oats, baking powder, baking soda and salt in large bowl.
Beat butter and sugar in second large bowl until smooth. Beat in eggs, one at a time. Add vanilla and rind; beat just until combined. Beat in milk.
Make well in center of flour mixture. Add egg mixture to well; stir to moisten flour mixture. Fold in berries, nuts. Divide into muffin cups.
Bake in 375°F oven 17 to 19 minutes, until pick tests clean. Turn out onto rack; let cool completely.
Mix sugar and cream until smooth. Drizzle over muffins.