When I cook onions and don't want to use fat, I use cooking spray on the skillet and put the lid on as soon as I add the onions to the pan. The cooking spray keeps it from sticking and the lid traps in the moisture so they steam and don't dry out. I'd imagine using water or broth would be similar except I like to brown the onions a bit which wouldn't happen if you have too much moisture in the pan. Either way, I'm sure they would taste delicious and have little fat in them.
Highest weight ever (Aug 1991): 240 lbs
Recent FitDay reboot starting weight (Feb 2017): 155 lbs
Current weight: 148.5 lbs
Goal weight: 145 lbs