Sift the first 5 ingredients together in a small bowl and set aside.
Mix water and oatmeal together in a small bowl, set aside and allow to cool for 15 minutes.
Cream unsalted butter, brown sugar and sugar together until light and fluffy. Add eggs and vanilla to creamed mixture, mix well.
On low speed, gradually add dry ingredients to wet ingredients, scraping down sides and bottom of bowl. Mix well until all ingredients are incorporated, but take care not to over mix. Add oatmeal mixture and continue to mix. Pour batter into a greased and floured baking pan. Bake at 350° for at least 25 minutes, depending on type and size of baking pan used. Cake is done when a wooded skewer inserted into the center of the cake comes out clean. Remove from oven to a cooling rack. Cool completely before adding topping.
In a medium bowl, mix butter and brown sugar until creamy. Whisk heavy cream into mixture and blend thoroughly. Add pecans and coconut to mixture and blend well. Spread topping over cooled cake. Place under broiler unit of oven. Brown until a light golden color. Be careful! This step takes very little time.