Cook the potatoes in a microwave until fork tender, about 10 to 15 minutes on high. Remove and let cool completely.

Meanwhile, brown the sausage in a skillet, crumbling with a wooden spoon. Stir in the onions, mushrooms and a bit of garlic salt and pepper. Cook until browned, about 8 minutes. Remove from heat and set aside.

Preheat oven to 375 degrees F. Line a baking sheet or dish with foil (for easy cleanup).

Once the potatoes have cooled, slice in half, lengthwise, and scoop out the insides with a spoon. Make sure to leave a thin layer of potato in the shell. Transfer the potato filling to a large bowl, along with the sour cream, 1 cup of cheese, garlic salt, and pepper. Mash until somewhat smooth. Stir in the sausage mixture and parsley until well combined. Taste and adjust seasoning accordingly. Scoop the mixture back into the potato shells. Top with the remaining shredded cheese and bake until warmed through and golden brown, about 15 to 20 minutes.