Pour boiling water over oats, cover and let stand 20 minutes. Beat shortening and both sugars together until light and fluffy. Blend in eggs and vanilla. Add oats mixture and mix well. Sift together flour, cinnamon, soda, salt and nutmeg. Add to other mixture and mix well. Pour into well greased and floured 9" square baking pan. Bake 50 to 55 minutes in 350° oven. Do not remove from pan. Spread frosting evenly over cake.
Combine ingredients and boil until bubbly. Spread on cake.