Once the burgers are cooked, reduce heat in the same skillet to medium and add ghee to melt. Once ghee is melted, add onions and cook, stirring, until tender, about 4 minutes and scraping up any brown bits in the bottom of the skillet. Season with salt, pepper, garlic powder, onion powder, cajun seasoning and dried thyme.
When the onions are very tender add the mushrooms and stir to combine and cook, stirring, for about 2 more minutes to develop some flavor on the mushrooms. Add arrowroot starch and stir until well-combined into the onion mixture. Reduce heat to a simmer and add the beef broth, coconut aminos, yellow mustard, apple cider vinegar and continue to cook, stirring, until the sauce thickens and all flavors are combined, 4 to 5 more minutes.
Return the hamburger steaks to the skillet and laddle gravy over the burgers. Top with parsley and serve. Enjoy!