i'm in psychology, so it obviously might be different for your discipline, but otherwise I was in a similar position - when I did this recently I didn't have any data to show them or anything like that.
because of that, their focus was on finding out what I had done so far and what I planned to do in the future. Basically to see if what I planned to do was achievable and practical, and could realistically be completed within the 3 years.
one of the questions they ask in my discipline which I think they tend to ask most people is why is your project worthy of funding? It obviously is because you've got funding for it - but you just need to briefly describe why your area of research is important and relevant.
but my key tip is just to try and relax as much as possible - i found that nerves got the better of me a bit, and made me ramble a bit, and fill lots of gaps with eh...! so just be clear about what you've done, what you plan to do and why, and how it can be done in the timescales.
good luck!