How do I pick my dissertation topic?

[bigtrees]

I am a non-traditional applicant, considering pursuing a 100% online PhD in Systems Engineering from Colorado State University. If I move forward, I'll be funded by my employer. 

I've reached out to a professor at CSU, who might be my advisor, and his response when I inquired about potential dissertation topics is that I can pretty much pick anything related to systems engineering, but it should be something that I have passion for and am highly interested in. This is a bit of a quandary for me, I was more hoping that there would be a list of potential topics and I could pick the most interesting one.

Since that is not the case, and I am on my own to find and propose a dissertation topic, any suggestions about how I go about doing just that?