Cook the bacon over medium heat until nice and golden. Drain the fat and set the bacon aside.
Add the onions and mushrooms to the skillet till the veggies are soft.
Grease an oven proof casserole and add the hash browns at the bottom. Season it with garlic salt, salt and pepper. Crumble the cooked bacon and add on top. Layer the veggies.
Now, in another bowl, beat together eggs, milk and parsley. Pour the mixture into the casserole. Sprinkle cheese on top and leave it to set in the fridge overnight.
Pre-heat the oven to a good 200 degrees C. Bake for an hour or until set. Serve hot.