Having to write a creative essay about a serious topic can be a very challenging assignment for most writers. That is because many academic essay topics can be very straightforward and leave little room for any creative details. However, since you are able to choose between a few different types of essay, you are in a great position to add some creative details. Of the three alternatives you listed, lesson plan, clinical intervention, or design study, we think that a clinical intervention gives you the greatest opportunity to show off your creative streak. That is because a clinical intervention allows you to create a hypothetical client who is in need of treatment.
You can start your clinical intervention in either of two ways. You can start by introducing the problem(s) that you want to address with the intervention. You want to broadly define the problem and give basic information about it, such as its prevalence and groups that are at risk. Because you are apparently working with specific units, you want to draw the problem(s) that your fictional client is facing from the information covered in your units. You could also start by giving an introduction to your fictional character.
Whichever way you choose to start, the other section should come second. You want to demonstrate academic knowledge about the topic and introduce your reader to your fictional client. You need to give enough details about your fictional character for the reader to understand them. Age, gender, family situation, living situation, race, and socioeconomic factors are all issues that impact qualify of life, potential community resources, and support systems. Therefore, they need to be included in your description, as well a description of the event(s) that prompted an intervention.