In a bowl, mash bananas almost to a puree.
Combine boiling water and shortening in another bowl; stir to melt the shortening.
Add to mashed bananas.
Add banana flavoring and set aside until lukewarm.
In a cup, dissolve yeast in lukewarm water.
Stir into banana mixture.
Add 1 c. (250 mL) of the flour and beat until smooth.
Gradually add half of the remaining flour; continue beating to make a smooth sponge.
Allow to rest for 10 minutes.
Beat in remaining flour.
Cover dough and allow to double in size.
Turn into well-greased loaf pans.
Cover and allow dough to just come to top of pans.
Bake at 350°F (175°C) for 15 minutes or until loaf tops are rounded.
Increase heat to 400°F (200°C) and bake for 30 to 40 minutes more. (Baking time may vary with the size pans you use.) Bread should be golden brown and sound hollow when you tap the top of the loaf.
Brush lightly with small amount of low-calorie margarine.
Cool on rack.