Joined a lab, picked a subfield but lost on what my specific project is

How did you come up with your dissertation ideas/direction? I’m close to the end of my first year and I finally joined a lab two months ago. I’m leading the data collection for a grant funded project that I’m very interested in, but I have the flexibility to have my own focus and project due to a fellowship I won. Because of this my advisors have been asking me what my vision is for my dissertation but I don’t think I can be specific enough. I feel there is so much for me to learn in this subfield and also so pressured to design a new study and have a specific focus already. I feel so behind and spread thin! Any one have any advice? I feel like reading literature is a great way but finding the time between data collection and full class schedule is like impossible.

US BME PhD