Designing the evaluation approach and method
You need to design an evaluation approach and method that is fit for purpose. It is important to be practical about what you can realistically do in the evaluation, and that your research design will deliver the information you need to make evidence-based judgements about the outcomes and impacts of the intervention.
The evaluation design needs to gather detailed information about how the intervention has worked and what its impact has been, including (where possible) calculating the return on investment. Without this kind of information there is no proof that what has been delivered is effective or delivers value for money.