Mash the ripe bananas in a large bowl until mostly smooth.
Gently warm the nut butter and honey or maple syrup until smooth and pourable.
Add the warm mixture to the bananas, then stir in cocoa powder, vanilla extract, and salt.
Fold in the rolled oats until evenly combined. Stir in chocolate chips if using.
Press the mixture firmly into a parchment-lined 8×8-inch pan.
Refrigerate for at least 1 hour, or until fully set.
Slice into squares and serve.