The art of substitution is easy in baked goods. With mashed bananas, you don't need to add eggs.
Preheat the oven to 350 degrees F. Cream the margarine and sugar together, then stir in the flour, baking powder, and baking soda. Add the remaining ingredients and mix well.
Pour into an oiled 8 1/2-inch-by-4 1/2-inch bread pan and bake for 50 minutes.