Preheat oven to 350 °F. Line a 9x13" pan with aluminum foil, and grease foil (bottom and sides) with shortening.
Whisk protein powder, flours, salt, and xanthan gum together. In separate bowl, mix bananas, juice, molasses and sugar. Add eggs and whisk together until eggs are thoroughly incorporated. Add sunflower seed butter, and whisk until fairly smooth (a few blobs are OK).
Combine wet and dry ingredients. (A silicone/wooden spoon is most useful here.) Add approximately 5 ounces of chocolate chips, if desired and stir well.
Turn batter out into prepared pan. Using a wet or oiled hand, press batter into corners, and lightly smooth top. (It will be very thick and gooey--almost the consistency of a cookie dough.) Bake for 30-35 minutes, until a toothpick will come out clean.
Remove pan from oven, and let sit on cooling rack about 30 minutes. Slide foil lining out of pan onto cooling rack, and peel sides of foil away from bars. Let cool completely, then cut into bars/squares and remove from foil. Store in airtight container (cupboard or fridge).
For chocolate chip version: Turn off oven. Top with remaining chocolate chips, and place pan back in oven until chips soften. Spread chips over top of bars, and allow to cool as above. When storing, place a piece of waxed or parchment paper between layers so chocolate top doesn't get runny.
When I cut the bars, I place the pan so that the long sides are facing me. I cut down the center longways, and then into about 1" bars (2 rows of 8-10 bars) and serve for snacks. If you wanted them as a meal replacer (like a breakfast bar) you could cut them slightly wider so you only got 12-14 bars/pan. A long knife works well; a pizza cutter works even better.
I used palm shortening (Spectrum), but soy-based ones will work as well.
The eggs are used to as a binder; to make egg-free, add another banana or 1/2 cup applesauce. You may need to increase baking time to compensate for extra moisture.