Thaw out your ground turkey if it's frozen. 1 pound will make 5 thin burgers, so it will serve 2-3 people depending on their size/appetite.
Preheat large frying pan. I used a cast iron and a nonstick simultaneously to make lots of burgers at once, and both worked fine (make sure your cast iron is seasoned!). If you wanted and were able to, I think cooking these in a buttered pan would add to their deliciousness. We just can't all eat butter around here, so that's why my recipes are all dairy free as well as being gluten and egg free.
Cut 1 lb. ground turkey (ours was 85/15) into 5 patties and smush them very thin. Place them into frying pan and smush down, thin out to less than 1/2" thick and larger in diameter than a standard hamburger bun.
Thinly slice onion (white, yellow, Vidalia, etc) and PILE on top of cooking burgers and salt and pepper them.
When juices are starting to pile up on top of burger and underside is browned (see middle pic above), carefully flip the whole burger so it's on top of the onion pile. Cook thoroughly, allowing onions to brown/carmelize.
Serve while hot with your choice of condiments. Would be great on a huge leaf of lettuce, but we didn't have any so we ate them plain with ketchup and loved them. I will be honest and warn you, I found this recipe to be yummy enough that I will definitely make it again, but the leftovers lack the same flavor by far, so try to make what you'll consume. Otherwise, if you can have eggs,throw leftovers in an omlette, or use them for a soup if you're avoiding eggs. :)
I know these look very simple and plain, but they are tender, juicy and a great change from the norm.