(THIS APPROACH IS NOT FOR REMEMBERING TRAUMATIC NIGHTMARES--SEE PTSD HELP)
I don't believe that a banana in your dream has the same meaning for every person from every culture. Its significance is unique to you! The focus should be on what each element of your dream or nightmare means personally to you. Find a friend who can listen without forming preconceived notions about your experience. Share your entire nightmare with all its gory and reprehensible details. If a friend can't handle this, consider seeing a professional therapist.
The person you share with should ask, "What was the most important part of the nightmare? What stood out to you?" Being in a deeply relaxed state can help keep your conscious mind from dismissing the exercise. Then, try embodying that most important part of your dream. Spend some time getting into character as if you are acting in a play. If it's the banana, then you become the banana. Talk to yourself as the banana, expressing what you think and feel about yourself.
Ask the banana questions like: Why are you here? What do I have to learn from you? What will it take to get you to stop haunting me? Be open and let the banana "talk" to you, sharing something you need to hear. Write it down if it helps. This message is the important lesson from your nightmare that keeps it recurring.
Write down what the banana says you need to do to stop it from appearing in your sleep. See how this advice relates to your current life. It might be obvious, or, if it's something deeply repressed, your friend might recognize it. Either way, take the advice. Thank the wise banana for its insight and ask for more guidance in future dreams, which may be less nightmarish.
Keep a strict dream journal, following advice on this site, and observe how your dreams and nightmares evolve and become less impactful in your life.