Heat oil in a small pan. Saute the bananas unti golden brown and remove from the pan. There should be enough oil left to grill the bread (grillled cheese style), but you can add it to the bread or reheat in the pan. 

Slather the nut butter on one piece of the bread. Evenly distribute the banana on top of the nut butter and add the second piece of bread. Grill in pan for a couple minutes on each side.

It aint healthy, but it sure is tasty.