Line a square (8x8) pan with a large piece of parchment paper (enough so the parchment sticks up around all the sides).
Mash bananas with a fork until creamy and sticky and most or all chunks are gone.
Stir in remaining ingredients and combine well.
Pour mix into pan and spread out evenly and pack down firm. (I do a sort-of windshield wiper motion.)
Bake 10-12 minutes, until golden, firm and crisp. (You can lift the parchment paper up to assess the edges and the bars pretty easily, just be careful not to burn yourself!)
Lift out and place on a cooling rack.
Once cool, cut 10 equal pieces.
Wrap each individually in plastic wrap.
Place wrapped bars in a freezer bag and freeze.
Reheating: I like these best when you let them thaw naturally (takes about an hour) but you can reheat for a few seconds in the microwave, they'll just be chewier and softer that way. Thawing allows them to stay fairly crisp.
Chef's Note: If you want to add raisins or mini chocolate chips, add ¼-cup and reduce instant oats to ¼-cup.