Preheat oven to 350°.
Coat a 9-inch round cake pan with cooking spray, and line bottom of pan with wax paper. Coat the wax paper with cooking spray.
To prepare cake, combine dates, 1/2 cup cocoa, 1/2 cup boiling water, and 1 teaspoon coffee granules; let stand 20 minutes. Place bread in a food processor, and pulse 10 times or until coarse crumbs form to measure 1/2 cup. Place crumbs in a large bowl. Reserve 10 walnut halves for garnish. Lightly spoon the flour into a dry measuring cup, and level with a knife. Combine remaining walnuts, flour, and salt in food processor, and process until finely ground. Add to breadcrumbs. Place date mixture, 1/3 cup granulated sugar, oil, 1 teaspoon vanilla, and egg in food processor, and process until smooth, scraping the sides of bowl once. Add date mixture to breadcrumb mixture, stirring well.
Beat egg whites with a mixer at high speed until soft peaks form. Gradually add 1/3 cup granulated sugar, 1 tablespoon at a time, beating until stiff peaks form. Gently stir one-fourth of the egg white mixture into batter; gently fold in the remaining egg white mixture. Spread batter into prepared pan. Bake at 350° for 25 minutes or until cake springs back when lightly touched. Cool in pan for 10 minutes on a wire rack, and remove from pan. Remove the wax paper. Cool completely on wire rack.
To prepare glaze, combine 1/3 cup cocoa and the next 4 ingredients (cocoa through 1 teaspoon coffee granules), stirring until smooth. Stir in 1/2 teaspoon vanilla. Cover and chill for 1 hour. Gradually add powdered sugar to the cocoa mixture, beating with a mixer at medium speed until smooth and thick.
Place cake layer on a plate. Spread the glaze evenly over top and sides of cake. Arrange reserved walnut halves on top.