For cake, preheat oven to 325 degrees F. Generously coat a 10-inch nonstick fluted tube pan with cooking spray; set aside. In a medium bowl combine all-purpose flour, white whole wheat flour, baking powder, pumpkin pie spice, orange peel, and salt; set aside. In a small bowl combine the water and pumpkin.
In a large bowl combine the 1 cup sugar, the oil, and the 1 teaspoon flavoring. Beat with an electric mixer on medium-high speed until well mixed. Add egg whites, one at a time, beating well after each addition. Alternately add flour mixture and pumpkin mixture to beaten mixture, beating on low speed after each addition just until combined.
Sprinkle pecans in the bottom of the prepared tube pan. Carefully pour batter evenly over pecans. Bake for 45 to 50 minutes or until a wooden pick inserted in center of cake comes out clean. Cool in pan on a wire rack for 20 minutes. Invert pan and cake together. Remove pan. Cool cake on wire rack for at least 2 hours.
Meanwhile, for glaze, in a small saucepan combine orange juice, the 2 tablespoons sugar, and the cornstarch; stir until cornstarch is completely dissolved. Cook and stir over medium-high heat until boiling; cook and stir for 1 minute more. Remove from heat. Stir in the 1/4 teaspoon flavoring. Cool completely.
Just before serving, drizzle cooled glaze evenly over top of cooled cake. If desired, garnish with orange slices.