Sieve together the flour, baking powder and salt. Add oats. Put sugar, treacle and margarine into a saucepan and heat gently until margarine has melted. Add to the dry ingredients and mix well. Press the mixture into a greased 7inch sandwich tin and mark into 8 wedges. Sprinkle with coarse oatmeal. Bake in a moderate oven, 350°F., Gas Mark 4, for about 20 minutes.