In a large bowl, combine the oats and boiling water. Let stand for 15 minutes or until cooled.
In another large bowl, cream butter and sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Add the oat mixture; mix well. Combine the flour, cocoa, baking soda and salt; add to creamed mixture and mix well.
Transfer to a greased 13x9-in. baking pan. Bake at 350° for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Combine the topping ingredients; spoon over top of warm cake; broil about 4 in. from heat for 3-4 minutes, or until top is lightly browned.