Grease a 13x9x2-inch baking pan. Set aside.
In small bowl, combine oats and boiling water; let stand 20 minutes. In medium bowl, combine flour, cinnamon, baking soda, and salt.
In large bowl, beat granulated sugar, the 1 cup brown sugar, and the shortening on medium speed of electric mixer until combined. Beat in eggs. Beat in oatmeal mixture.
Gradually add flour mixture, beating until combined (if necessary, stir in last portion by hand). Turn the batter into prepared pan.
Bake in a 350 degree F oven for 30 to 40 minutes or until wooden pick inserted in center comes out clean. Place pan on wire rack.
In saucepan, combine butter, coconut, the 2/3 cup brown sugar, and the milk Cook and stir until boiling. Stir in walnuts. Spoon over hot cake. Cool. Makes 16 servings.