Preheat oven to 450 degrees. Coat a large baking sheet with cooking spray.
In a large bowl, combine flour, granulated sugar, brown sugar, baking powder, baking soda, and salt. Cut in butter until flour mixture resembles coarse crumbs. Make a well in center.
Combine buttermilk, egg, and peel; add all at once to flour mixture. Stir with fork just until moistened.
Toss berries with cornstarch to coat; add to flour mixture. Stir gently 3 to 5 turns, just until berries are incorporated (do not overmix).
Using a large spoon, drop dough into the 12 mounds on baking sheet, leaving 1 inch between mounds.
Bake 12 or 15 minutes or until tops are golden.
For icing, in a small bowl whisk enough lime juice into powdered sugar until drizzling consistency. Drizzle over warm scones. Sprinkle with nuts. Serve warm.
