Combine flours , baking powder, baking soda and salt in a large bowl.
Mash bananas, combine with sweetener, melted margarine and egg. Stir well.
Mix the dry ingredients with a banana mix. Knead with a wooden spoon until you have a uniform mix.
Pour batter into an loaf pan. Bake at 350° for 50 to 55 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes; remove from pan, and cool completely on wire rack.
Cool in pan on a wire rack 10 minutes; remove from pan, and cool completely on wire rack.