I'm making a cake using chcolate ganache and sliced bananas as the filling; I know about lemon juice on bananas and apples to keep them from turning brown; does this still apply if the bananas are covered with the top layer of cake? If so, will the bananas have a lemon taste?
The taste will be fine. Just keep in mind that the bananas will deteriorate much faster than the cake. They will still take on that strong, old taste within 24 hours.