Combine boiling water, oats, and butter in a large mixing bowl, stirring well. Let stand 20 minutes. Add sugar and eggs, beating well.
Combine flour, soda, and cinnamon; stir well. Add to oats mixture, stirring well.
Pour batter into a greased 13- x 9- x 2-inch baking pan. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean.
Spoon Coconut Topping over warm cake. Broil 4 inches from heating element 2 minutes or until browned. Cut into 2-inch squares. Serve warm or cold.