Place a large skillet over medium heat. Add ground beef to pan and cook for 8 to 10 minutes, until no longer pink. Break up the beef at it cooks. Drain excess grease and set aside.
In a large mixing bowl, combine onion, bell pepper, mushrooms, Worcestershire sauce, cream cheese, sour cream, and milk. Set aside.
Add ground beef to vegetable mixture and stir to combine.
Add the hash browns to a 9-inch x 13-inch baking dish, and spread out into an even layer.
Place 6 slices of provolone and 6 slices of mozzarella on top of the potatoes to cover the layer.
Add ground beef mixture over the cheese and spread into an even layer. Top the casserole with 6 slices of each cheese.
Cover the baking dish with foil so the cheese doesn't burn.
Bake for 40 minutes. Carefully remove the foil from the pan and bake for another 10 minutes to get the cheese golden and bubbly.
Remove from the oven and cut into 8 portions. Serve warm.
Notes
I buy a 32-ounce bag of frozen cubed hash browns, use 3/4 of the bag for this recipe, and then save the rest for breakfast.