Add extra virgin olive oil to a large skillet over medium heat. Add mushrooms and onions. Cook, stirring often, for about 10 to 15 minutes, or until onions are softened and starting to caramelize. Season, to taste, with salt and pepper. Remove from heat.
In a large bowl, add ground beef and BBQ seasoning. Mix together. I find using clean hands works the best to combine everything.
How to Stuff Burgers with The Stuffer from House of BBQ Experts
Using a Burger Press, create your stuffed burgers. I recommend getting The Stuffer from House of BBQ Experts.
Choose the regular size base (½ lb) at the bottom of the press.
Fill the press about ¾ full with the beef.
Press the meat with the small end of the press to make an indent for the fillings.
Fill with cooked mushrooms, onions and cheese.
Place more ground beef on top of the filling. Use the other end of the Stuffer to press and seal the meat.
How to Grill
Heat an oiled grill to medium heat. Add burgers. Grill for 6 minutes on each side.