You want to seem keen and flexible and show that you are happy to fit in with the department's teaching requirements but they also want to hear about new courses that you would like to offer. In order to answer this question you need to look at the department's current undergraduate curriculum. That way you can be sure the courses you have invented will fit in with what they offer now. So if the department already has a course on Nazi Germany, do not propose to offer a new one. You have to be careful here: do not let your creativity run away with you. If you do get the job, your new colleagues might say 'I loved that course you proposed in your interview, can you run it next year?'