Preheat the oven to 350 degrees. In a medium size bowl combine all dry ingredients (flour, baking powder, baking soda, and salt), stir together to combine.
In another medium size bowl combine margarine and sugar, with a mixer cream the margarine, and sugar together until light and fluffy.
Add in mashed bananas, eggs, milk and mix well.
Add 1/2 of the dry ingredients into the wet ingredients, mix until the flour is just mixed in, then add in the remaining flour and 1/2 cup walnuts, blend together until everything is mixed together. Do not overstir.
Pour batter into a greased 8×4 inch loaf pan. Then top the batter with the remaining chopped walnuts.
Bake at 350 degrees for 55 to 60 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes on a wire rack.