Hi Amy,
I think you need to come up with a theme or a language point that you want to teach. It's hard to suggest something for you with so little information.
Some starting points that I would recommend are:
-Pick a topic such as food, travel, hobbies, future goals and dreams, and look for some short conversational activities online that focus on your topic.
-Pick a grammar point or language feature such as a particular tense, phrasal verbs, reported speech, ways of giving your opinion etc. Make sure you really understand how the language feature works and what the rules for its usage are.
-Then make a plan that combines your topic with the language feature you want to cover. So for example if you are covering hobbies, you can ask your 'student' to use adverbs of frequency (often, never, sometimes).
Keep it short, sweet and simple and if you find a good idea online don't be afraid to use it. In my experience, interviewers are looking to see how well you can explain ideas and interact with others, not how original your lesson ideas are.
Charlotte