Preheat oven to 350 degrees.
Use a 9-by-5-inch nonstick loaf pan or line a loaf pan with a baking pan liner or lightly spray with vegetable cooking spray.
Place prunes and water in a food processor or blender and puree.
Place bananas in a large bowl and mash.
Beat together the prune puree, egg whites, lemon juice, and milk.
In a separate bowl combine the flour, sugar, baking powder, and salt, if using.
Stir the wet ingredients into the dry ingredients until just moistened.
Transfer batter to loaf pan.
Bake for 1 hour and 15 minutes or until a wooden pick inserted in the center of loaf comes out clean.
Cool in the pan for 10 minutes.
Remove and finish cooling on a wire rack.
Slice into 12 slices.
Variation â–  Substitute 1 teaspoon vanilla and 1 teaspoon ground cinnamon for the lemon juice.