Cut sweet potato into thin slices, about ¼ inch (6 mm) thick.
Place in toaster and set it to the maximum cook time. When it pops, flip the sweet potato slices over and toast 1 more time. Depending on the strength of your toaster and your preferences, you may need to toast it 1 more time after that.
Remove from toaster and let cool enough to handle.
Spread peanut butter evenly across sweet potato toast and top with sliced banana.