Preheat the oven to 350 degrees. Butter an 11- by 7-inch baking dish. Place the oats in a medium bowl and cover with the boiling water; let stand for 20 minutes. Meanwhile, cream together the sugars, shortening and eggs in a large bowl; add the vanilla and mix to combine. In a separate bowl, sift together the flour, baking soda, cinnamon and salt. Mix the dry ingredients into the creamed mixture until well combined; stir in the softened oats. Pour into the prepared dish and bake for 30 minutes. While the cake is baking, mix together the topping ingredients in a small bowl. Remove the cake from the oven and spread the topping over the cake while it is hot. Place under the broiler for 1 to 2 minutes or until lightly browned. Let the cake cool slightly before serving.