Heat oil in a frying pan over low heat. Add onions. Stir around the pan and cook for 10 to 12 minutes until it gets nicely browned. Set aside.
Beef Mushroom Burger
In a large bowl, combine beef, chopped mushrooms, egg, salt and pepper, Worcestershire sauce and garlic powder. Mix with a large spoon or your hands.
Divide into 4 equal portions depending of the size of the bread you will be putting them on. Shape into hamburger patties and make a dimple in the center of each patty (see video).
Heat oil in a frying pan over medium heat. Fry the patties 4 to 5 minutes on each side or until well done.
Meanwhile, toast the cut side of the buns lightly.
Serve the burger: Spread your choice of sauce on the base of the buns. Add the mushroom burger patty, top with cheese and fried onions. Top with the other half of the bun. Serve immediately!
Video
Notes
You may cook the onions and the burger patties side by side to save time.
I used portobello mushrooms in this recipe. White and brown button mushrooms are good alternatives.
There's a bonus clip at the end of the video about the dressing I used for the burger. We usually just use mayo-ketchup for burger nights but since I have a big bottle of sriracha sitting in the fridge and I happen to be craving for something spicy, that's what I used.