Its a push latch.
push the fuel door in to open, push the door in to close.
Also, there is no gas cap.
Also, there is a special fuel filler nozzle hidden under the trunk carpet just behind the driver rear seat (fold down the rear seat to access). You need that if you ever need to add fuel from a gas can.
I just accidently discovered this feature watching a Lincoln online video.
I thought I read the manual in detail. I learned what kind of fuel, how to insert nozzle, what to do if you run out of gas etc. All these answers were after the lid was opened. Couldn't find anything on how to open the lid. Now that I have the answer I really feel dumb for not trying that.
The trunk lid of a Lincoln MKZ is nearly impossible to pry open, especially during the winter months. Last year, I used soccer net ties. However, the ties were already worn out and fell apart by winter's end. This year, I used a cut up power cord (like from an old cordless phone or similar)