Dont do this! If you put pieces of bananas and other fruit into your soil its just going to rot. The rotting of the fruit could release a deadly concoction of bacteria and stuff.
Now what you could do is get a cup of water and put some blended banana into the water to dilute it. Pour the water/banana puree in the dirt and some is going to settle. But this can still cause rot of the fruit.
So what you do is one day after you pour the water/banana puree into the dirt, the next day make sure your pour a lot of water to push the puree down the dirt and to flush it a little.
Just smell the top of your dirt after this and if it doesn't smell bad your in the good. If it smells bad after awhile flush your soil with water or transplant...it fun to experiment.