Questionnaire request flow

In FHIR, how do you request a questionnaire to be filled in by a patient?

Furthermore, can you use the CarePlan resource to define a plan where after 3 months questionnaire X needs to be completed and after 6 months, questionnaire Y needs to be completed? Which resources are to be used and what are the links between them?

Thank you for your guidance.

The simplest way is to use Task, though ProcedureRequest would also be legitimate (answering for STU3). You can use CarePlan, but CarePlan doesn’t support complex timing relationships. For those, look to ReqeustGroup