To prepare crumb mixture, place the bread in a food processor; pulse 10 times or until coarse crumbs form to measure 3/4 cup. Combine breadcrumbs, walnuts, and next 3 ingredients (walnuts through cinnamon) in a small bowl.
To prepare cake, combine the flour, baking powder, baking soda, and salt in a medium bowl. Combine 3/4 cup sugar, shortening, rind, and vanilla in a large bowl, and beat with a mixer at high speed until well-blended. Add the flour mixture to the shortening mixture alternately with buttermilk, beginning and ending with the flour mixture. Spread the batter into an 8-inch square baking pan coated with cooking spray. Sprinkle the batter with the crumb mixture.
Bake at 325° for 45 minutes or until cake begins to pull away from sides of pan.