Combine all ingredients through the parsley and form into 5 hamburger patties.
Heat a cast iron skillet on medium heat. Add the oil and the butter, and once hot, add the turkey burgers and the onions. Cook for 5 - 6 minutes per side mixing the onions around. Once the burgers are cooked, alternately top each patty with either the smoked gouda or the cheddar cheese. Let rest for a minute.
To finish the burger, use your favorite gluten free bun. Add a piece of lettuce. Stack the burgers (We ate only one burger at a time) and top with as much of the onions as you will enjoy. I added BBQ sauce and pickles. Now that is a burger.
Serve and enjou.