Preheat the oven to 350 degrees Fahrenheit.
In a large bowl, gently mix together the ground beef, Worcestershire sauce, seasoning salt and egg. Do not over mix.
Form the beef mixture into 4 patties. Refrigerate the patties while you prepare the other ingredients.
Melt the butter in a large skillet over medium high heat.
Add the onions to the pan. Sauté for 3-4 minutes, stirring occasionally.
Then stir in the sliced mushrooms. Season the mixture with salt and pepper.
Sauté for 3-4 more minutes until the onions and mushrooms are soft and start to brown. Remove the mixture from the pan to a separate plate.
Then add the beef patties to the pan and brown each sides of the patties (2-3 minutes per side).
Transfer the patties to a baking dish. Top each patty with the mushroom and onion mixture.
Cook for 8-10 minutes until the patties are cooked through.
Top each patty with the shredded Monterey Jack Cheese. Cook in the oven for 1-2 more minutes until the cheese is melted.
Remove from the oven, serve warm and enjoy!
