In a large bowl, beat oil and sugar until blended. Beat in egg whites. Combine the flour, cocoa, baking powder and salt; gradually add to sugar mixture just until moistened. Stir in vanilla. (Batter will be thick).
Spread batter into a 9-in. square pan coated with cooking spray. Bake at 350° for 20 to 25 minutes or until a toothpick inserted in the center comes out clean. Cool 10 minutes on a wire rack. Spread with jam and sprinkle with Grape-Nuts if desired. Cool completely.