Coat an 8-inch round cake pan with cooking spray; dust with 2 teaspoons flour, and set aside.
Bring 1% low-fat milk to a simmer in a small saucepan; stir in 1/4 cup oats. Bring mixture to a boil, and remove from heat. Spoon mixture into a small bowl; let cool.
Combine 3/4 cup flour, baking powder, cinnamon, and salt in a small bowl; set aside. Combine 1/2 cup granulated sugar and 2 tablespoons softened margarine in a large bowl; beat at medium speed of a mixer until blended. Add applesauce, vanilla, and egg; beat until blended. Add flour mixture and oatmeal mixture; beat until well-blended. Pour batter into prepared pan. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Remove from oven; set aside on a wire rack.
Combine the brown sugar, evaporated milk, and 1 tablespoon margarine in a small saucepan; bring to a boil over medium heat, and cook 30 seconds. Stir in 1/4 cup oats, walnuts, and coconut; cook 30 seconds. Spread over cake; broil 2 minutes or until lightly browned. Let cool.