[timbit42]

My father solved this problem before I was born in 1969. Peel the top of the banana as if you are going to eat it. Put peanut butter on the knife and wipe it on the top of the banana. Take a bite. Continue until the banana is gone. Ignore the bread. It more keto that way anyway.

If you really want to use the bread, mash the banana and spread it on one slice, spread the peanut butter on the other and put them together.

[alanbernstein]

There's something just a bit different about the sensation of biting into a slice of banana, though.

[smegger001]

Or most optimal spread peanut butter on slice of bread fold bread around banana like a hotdog bun.